Caillou - A 4-year-old boy with a vivid imagination with friends and family who help him navigate the trials and tribulations of growing up. He wears blue longer shorts. In season 1, he is 3 years old (in a few episodes) and wore a gray shirt, but later he wore a yellow shirt. Caillou and his family live in a two-story blue house, whose address is mentioned in one episode as 17 Pine St. Caillou was first voiced by Bryn McAuley from 1997 through 2000, Jaclyn Linetsky from 2000 through 2003, and then Annie Bovaird.
Mommy - Caillou's mother. She is a busy homemaker most of the time but is seen to work in an office too. Caillou occasionally helps his mom with various chores and she often takes time to involve Caillou and his friends in activities such as crafts and baking. She is predominantly dressed in a red blouse with yellow trim, blue headband, blue ankle-length pants and blue shoes with green soles. Voiced by Jennifer Seguin.
Daddy - Caillou's father. He and Caillou occasionally work on projects around the house. He always wears a green sweater with red trim while at home. In the episode "Caillou The Chef" he says he once worked at a restaurant and made pizza. Voiced by Pat Fry.
Rosie (French name: Mousseline) Caillou's lively and adorable 2-year-old sister who is a typical toddler. She always wants to take part in the same activities as Caillou. In later seasons of the series she becomes more talkative and independent. She wears a blue dress, red socks and blue Mary Jane shoes. Rosie sometimes fights with Caillou, but they still love each other. She appears to be the only family member with red hair which had led most people to think she was adopted if not, it could be that Grandpa or Grandma that has had Red hair in their youth. Rosie was first voiced by Brigid Tierney, then Jesse Vinet.
Grandma - Caillou's paternal grandmother. Grandma is a very active adult who loves the arts and the outdoors. She passes that love on to Caillou. Grandma often comes up with creative ideas to solve Caillou's problems. She and Caillou paint and go birdwatching together. Voiced by Pauline Little.
Grandpa - Caillou's paternal grandfather. He takes Caillou on adventures, often going on walks and riding the bus throughout the town where they reside. In "Caillou's Hiding Place", he showed Caillou a hidden area inside a tree in the backyard. In the episode "Caillou Goes Camping", he and Caillou camp in the backyard. He is Daddy's father and loves to tell stories about Caillou’s Daddy when he was a little boy. He always wears a blue shirt. Voiced by George Morris.
Mr. Hinkle (French name: Monsieur Lajoie) - Caillou's neighbor, introduced in the 1998 episode "Caillou's Not Afraid Anymore". He has a gold tooth. In the episode "Farmer for the Day", it is said that his first name is Paul.
Leo - Leo started out as a bully in the 1999 episode "Caillou Goes to Daycare", but quickly befriended Caillou in the same episode. He is four years old like Caillou. They've been inseparable since. According to Caillou's Holiday Movie, Leo is Jewish and celebrates Hanukkah. That was meantioned back in 1999 in the episode "Caillou Goes To Daycare".
Clementine - Clementine was the first to befriend Caillou in the 1999 episode "Caillou Goes to Daycare". She is four years old like Caillou and Leo and can get rather bossy sometimes, but all in all she's pretty understanding. She is of Black Canadian heritage.
Sarah - Caillou first met her in "Caillou Goes Round the Block". She is 8 years old and already attends school. She is of Chinese heritage and celebrates Chinese New Year. She has a cousin in an episode where she invites Caillou to celebrate Chinese New Year. In another she invites him to school for "Bring Your Younger Siblings To School Day" because she has no siblings. Sarah has a pet cat named Olly and a dog named Murphy.
André - An orange-haired boy, aged 6, André is introduced in the episode "Caillou's Big Friend" and usually wears red sandals. According to the song "Days of the Week" released on the Caillou music CD Caillou and Friends, Caillou plays with him every Saturday. André enjoys biking and soccer.
Julie - Caillou & Rosie's teenage babysitter. She is 15, has blond hair, and enjoys playing with Caillou and Rosie.
Jason & Jeffrey - are identical twins. They enjoy eating pizza. Initially, they wore identically colored clothes. By Season 4, though, Jason started wearing a shirt with inverted colors, in order to tell them apart. They are both in Caillou's playschool class. The first episode they appeared in was "New House, New Neighbors"
Billy - Billy is Clementine's older brother. He is usually seen playing in a band with his friends or playing in sports. His age is unknown, but he appears to be at least 12 years old. In "Caillou Plays The Drum", It is revealed that he can play the drums.
Miss Martin - Caillou's teacher. She has red hair and always wears red overalls and a white long-sleeved blouse. According to the episode "Surprise For Ms. Martin" her birthday is in June. Her first name is Ann; this was revealed in "Caillou Goes to Daycare".
Jonas - A friend of Caillou's father. He lives on ranch and has a horse named Lucky. Jonas appears in 3 episodes and in Caillou's Holiday Movie.
Emma - A child in Caillou's playschool class who hates loud noises. It is revealed in a episode that she has Type 1 Diabetes.
Xavier - A child in Calliou's playschool class who usually wears blue overalls. At his birthday party, Caillou broke a piñata.
The puppet segments are used only on the PBS telecasts of Caillou, from 2000 to 2003 in order to fill the show's time slot. While Caillou has slots for commercials, and the English Teletoon shows ads during the breaks, PBS does not show paid advertising during the program. The newer shows do not include puppet segments.
Gilbert - Caillou's pet cat. He is the leader of the group. He has a greyish-blue body with black stripes and loathes dogs with a passion. He especially hates the bulldog in the neighbourhood. In the puppet segments of the program, Gilbert often composes odes. Puppeteered by Mike Petersen.
Rexy - Caillou's toy dinosaur. Bluish in color and speaks in a somewhat Hispanic accent, he is very playful. Rexy has the incapability to give a "good" hug. Rexy is noted for being rather pedantic. His speech impediment has been the scourge of his existence; he is often teased about it, and tends to react violently to any mention of it. Puppeteered by Kevin Yamada.
Teddy - An old teddy bear that once belonged to Caillou's daddy, and now belongs to Caillou, Teddy is reasonable, cute and brown. He is somewhat pessimistic, but all in all, he just needs a hug. Puppeteered by Frank Meschkuleit.
Diedi - A brown squirrel, she has a bushy tail, and is often seen playing with Rexy. Diedi first appeared as a baby squirrel when Rexy found on the ground lost from her family. Diedi lives in Caillou's backyard where most of the puppet segments take place. She was absent in Season 3. Puppeteered by Wendy Welch.
|Hot-Dog Man||The Hog-Dog Man is a person who only appears in the episode "Caillou and Daddy", in which he serves Caillou and his Dad with hot-dogs and mustard for their lunch. He is also a wrestler.||1|
|Pierre||Pierre is the leader for Camp Brome. Pierre was featured in the episode "Caillou Goes Camping".||1|
|The Doctor||Featuring in the episode "Caillou Visits the Doctor", she treats Caillou for an earache.||1|
|The Mailman||The Mailman was first featured in the episode "A Letter for Mommy", and later appeared in "All in a Day's Work".||2|
|Olly||Sarah's Pet cat. He appears in the episodes "Gilbert Goes to Vet", "Chinese New Year", "Sarah Goes to China". His last appearance was in the 2006 episode "Where's Gilbert?", shown in Caillou the Detective.||4|
|Rover||A dog that belongs to one of Grandma's friends.||2|
|Mr. Washington||A bus driver that drove Caillou's Dad to school many years ago.||1|
|Barbara||She is an old friend of Caillou's mom. She is blind, and appears in the episode "Dogs with Jobs".||1|
|Maxwell||Barbara's guide dog. He is a special dog and helps Barbara see where she is going. He appears in the episode "Dogs With Jobs".||1|
|Helen||One of Caillou's parents friends, she owns a boat.||1|
|Carol||A friend of Caillou's Mommy with whom she went to high-school. She appears in the episode "A House in the Sky".||1|
|Kevin||Carol's son. He appears in the episode "A House in the Sky".||1|
|Robbie||A boy who is deaf who only appears in the episode "Caillou and Robbie". He knows Sign language.||1|
|Allen||A child who went to Caillou's playschool one day to join the class. He is 5 years old and has Down's syndrome and a rather loud voice.||1|
|Frankie||A child who will live in the house Caillou's family helps build in the episode "Caillou's Building Adventure".||1|
|Sam||Frankie's father. He appears in the episode "Caillou's Building Adventure".||1|
|Evalyn||Robie's mother. She appears in the episode "Caillou and Robbie".||1|
|Bob||A plumber who fixes the pipes under Caillou's house. In a season 3 episode, he fixes the sink.||2|
|Kristen||Jonas wife. She only appears in the episode "Caillou's First Wedding".||1|
|George (imaginary friend)||Caillou's imaginary friend. He is never seen and only mentioned once.||1|
|George||Caillou's skating instructor who's really silly. He only appears in "Caillou's Skating Lesson".||1|
|George||Grandpa's friend. He only appears in "Grandpa's Friend". He is older than Grandpa and teaches Caillou how to play croquet.||1|
|Mary||A life guard who appears in the Season 4 episode "Caillou and the Big Slide".||1|
|Erik||A firefighter who rescues Gilbert from a tree. He is only seen in the episode "Caillou and the Fire Truck".||1|
|Stacy||A firefighter, she is only seen the episode "Caillou and the Fire Truck", although she is in Caillou's Holiday Movie.||1|
|Sparky||A Dalmatian at the fire station. He is seen in "Caillou and the Fire Truck" and "Caillou the Fire Fighter".||2|
|Emma||Grandma's friend. She lives on a sheep farm.||1|
|Mary||Emma's 10 year old daughter. She shows Caillou all that happened on the sheep farm.||1|
|Mr. Jenkins||One of Grandma's friends. He is allergic to Rover and lives at the nursing home. He appears in the episode "Grandma's Friends".||1|
|Mrs. Murphy||One of Grandma's friends. She has a granddaughter named Amy. She appears in the episode "Grandma's Friends".||1|
|Mrs. Wilson||One of Grandma's friends. She appears both times Grandma visits the nursing home.||2|
|Zoey||A zoo worker who shows Caillou different animals when he visits the zoo. She appears in the episode "Caillou Goes to the Zoo".||1|
|Brice||A photographer who takes a picture of Caillou and Rosie.||1|
|Henry||The Zamboni driver at the skating rink. He only appears in the episode "Caillou's Skating Lesson".||1|
|Chinook||A Husky who pulls a sled. She is seen when Caillou and his family go tobogganing.||1|
|Tammy||A child who uses a wheel chair. She is seen when Caillou goes swimming.||1|
|Lee-Juan||Sarah's cousin. She has only been seen in "Chinese New Year." She celebrates Chinese New Year with Sarah and her family.||1|
|Lee-Wun||A girl in Caillou's playschool class. She joins the class in "Deep Sea Caillou." She used to be shy but Caillou helped her feel better. She knows a lot about fish.||6|
|Stanley||The conductor on the train Caillou rides in the episode "Train Trip".||1|
|Nancy||Mr. Hinkle's sister. She owns a farm and appears in the episodes "Farmer for the Day" and "The Mystery Carrots".||2|
|Santa Claus||A Santa Claus in costume who appears in the episode "Holiday Magic". Rosie is afraid and not fond of him.||1|
|Vanessa||A librarian. She appears all 3 times Caillou goes to the library.||3|
|Bravo||A magician who only appears in the episode "Caillou the Magician".||1|
|Jack||A tow truck driver who tows Caillou's car and repairs it. The episode he appears in is "Backseat driver".||1|
|Emma's Dad||Emma's dad. He appears in the episode "Captain Caillou".||1|
|Rafiel||One of the skaters in Caillou skating class. She appears in the episode "Caillou's Skating Lesson".||1|
|Mrs. James||The owner of a pumpkin patch at which Grandpa and Caillou pick pumpkins. She appears in the episode "Pumpkin Patch Kid".||1|
|Lee-Wun||A kid in Caillou's playschool class that first appeared in the episode, "Deep Sea Caillou". She later makes cameos at the playschool.||6|
|Rocky||A lost dog. He appeared in the episode "Caillou and the Lost Puppy". Caillou called him Scruffy because he didn't know his name.||1|
|Dr. Orange||Gilbert's vet, He appears in the episode "Gilbert Goes to the Vet". He is also Olly's (Sarah's cat) vet.||1|
|Mara||A child who was in Caillou's playschool class when they play games at the park. She appears in the episode "Playschool Games".||1|
|Buddy||A hamster. He appears in the episode "Leo's Hamster" and has white fur.||1|
|Goldie||A goldfish. She appears in the episode "Clementine's New Pet".||1|
|The Captain||A Captain of a ferry that Caillou's family ride on in the episode "Caillou's Road Trip".||1|
|Jim||One of Caillou's friends he meets at the park. Jim appears in the episode "Caillou Makes a Friend". At first he didn't like Caillou, but soon became fast friends.||2|
|Bella||A dog that Sarah walks in the episode "Caillou Walks Around the Block".||1|
|Wendy||A child first seen in the episode "Caillou the Firefighter". She later makes cameos at Caillou's playschool.||7|
|Snowball||Nancy's (Mr. Hinkle's sister) rabbit. Snowball appears in the episode "The Mystery Carrots".||1|
|The Policeman||Seen in the episode "Caillou and the Police Officer". He gives someone a ticket for parking near a fire hydrant.||1|
|Lucky||Jonus' horse. He appears in the episodes "Cowboy Caillou" and "Caillou's First Wedding".||2|
|Herman||A goldfish that who appears in the episode "A Surprise for Ms. Martin".||1|
|Aunt Joan||Leo's Aunt. She appears in the episode "Leo's Lost Dinosouar".||1|
|Melanie||A child who appears in the episodes "Caillou the Spaceman" in season 2 and "Deep Sea Caillou" in Season 4.||2|
|Bernie||A parrot who appears in the episode "Where's Gilbert". He can talk and says "Keep an eye out for Gilbert".||1|
|Dylan||A brown dog that Billy walks. Dylan appears in the episode "Dogs with Jobs".||1|
|Fire Chief||Appears in the episode "Caillou the Fire Fighter". He is the fire chief and teaches Caillou's playschool class about fires.||1|
|The Pilot||Appears in the episode "Caillou Rides an Airplane". He shows Caillou the cockpit of the plane.||1|
|The Dentist||Appears in the episode "Caillou Goes to the Dentist".||1|