There are various tools (2-3 of them) but they're all different ones and don't work with eachother. Usually, a parent needs an easy to use panel to set screentimes, blocked sites, and which apps are allowed or not (and possibly a checkbox to allow the games subcategory every weekend). But all these tools, while exist, are separate and difficult to either install or make work properly.

I recently did a bug report at Linux Mint to create such an admin panel. While this was a feature request, I presented it as a bug, arguing that because of Mint's unique position as a "home" or "first" distro to new users, its absence is more like a bug. To my surprise, the creator of Mint, while not replying anything additionally, he assigned it a bug status, as if he agreed with the argument. So we might see something like it on Mint, but not for a couple of years yet... By that time you might not need it anymore, but I believe it'll come eventually to Linux too.