Karl's funny, but kids that are younger won't get his jokes.
The Ricky Gervais Show is just funny. Perfectly funny. Karl is so innocently misinformed, you can't help but laugh at his incredibile (and often impossible) stories. His friends poke fun at him, but always in a lighthearted sort of way, because obviously Karl needs a little bit of that to bring him back to earth. Though, I don't think that it's good to encourage kids to tease others like this, because it's not the same as in the show, so a little bit of an older audience is best. Besides, it'd be hard for younger kids to get the jokes.