Normal users should accept that if they let their kid play Angry Birds they’re risking an accident with all their other apps getting mucked with, and if they don’t like it they can buy five iPads.
https://support.apple.com/guide/deployment/shared-ipad-overv...
It’s only when you want to let them jump in and out of multiple apps (e.g. pick what game they want to play on their own) that you start having a problem.
(And the not-idiomatic-but-people-do-it-anyway solution for that, from what I’ve seen, is buying one extra iPad, and creating a special whole-family Apple account for it, to effectively serve as a game console for the kids.)
The solution to that is Assistive Access.
It’s more painful to use than it should be, but it absolutely solves this problem.