If you type in words like “spider-man”, “elsa”, “hulk” or even “superheroes” into YouTube, it’s safe to assume that the majority of content the video site’s algorithm serves up is probably decent.

My five- and seven-year-old constantly fight over who gets the iPad first. We have one, and they get to use it in tiny doses, usually when I'm at my wit's end. Their favorite app? ScratchJr, MIT's ...