Literally the worst thing to ever exist.
Cailou as a character is by far the most obnoxious little goblin I have ever encountered. I understand he's like 4 but that does not excuse any of his bratty misbehavior. He serves as an incredibly poor role model for children, teaching viewers that the best way to get what you want is to scream and cry and have your parents solve your problems for you.
If he was real, I would glady throw him into the sun.