If you're able to wrest control, you can have good experiences in sketchy apps. For example:
• Facebook with no Pages, just friends, sorted in chronological mode, and only subscribed to the particular friends that you actually want to know how they're doing.
• YouTube, but only for videos you find linked on some other place than YouTube; and then maybe subscribing to those videos' authors, and then directly checking your "latest updates" feed.
However, you can't really force kids to use these apps this way, and every step of these apps' workflows is trying to lead you out of this usage and back into their "idiomatic" recommendation-based one. So maybe better not to expose kids to the potential. (Or just give them an alternative interface without the drug-dealers-on-the-street-corners, e.g. YouTube videos discovered via an RSS reader, downloaded using youtube-dl, and loaded into Plex.)