This is the reason why Caillou is voiced by Dave.
Mickeymcguinness7: This is me again with another angry message. In the Caillou gets grounded series, people keep asking me why Caillou is voiced by Dave. You may think it's because he's too old but that's not why. Watch this video and you'll find why.
Teacher: Welcome to school. Caillou it's time to do a 500 page essay.
Caillou: No I will not do it!
Teacher: Caillou, you are expelled! Go home now!
Boris: Caillou, how dare you refuse to do your essay and got expelled! You are grounded for 12 weeks!
Doris: As for your punishment we're going to the hospital to get your voice changed!
Dora: Dad, I don't want to get voice surgery! I only want to stay home and watch the video where I caught you using the girl's bathroom!
Dad: Too bad, this is your punishment for busting me for using the girl's bathroom! Not only that, you tried to show your belly button in class and then you tried to do the same thing in detention and out in the community!
Slippy V: The doctor is here!
Boris: Can you change Caillou's voice because he got expelled from school for refusing to do his essay?
Caillou (Dave's voice): Now I sound more like Dave!
Boris: Caillou, you are grounded for 12 weeks!