The market remains flush with toys that poop: Gotta Go Flamingo, Poopsie Slime Surprise, Doggie Doo, Fishin' For Floaters. "It's a very light taboo," says Mary Higbe of Goliath Games.

The Super Soaker toy gun was on the top of nearly every kid's wish list in the '90s, and it made summer heat a literal blast. The game-changing toy has...