I love when kids make up their own words.
Colin's is "pompo." He uses it in make different contexts. Sometimes he substitutes words in a song: "Oh what fun it is to ride in a one-horse open pompo." Sometimes he uses it as an adjective "this toy is pompo. Other times he will call you a pompo.
Caleb's is "pishy." He uses it exclusively to describe something undesirable. If he doesn't like a food, if a toy doesn't work right, if you have not done something the way he wants.