My kids, 9 and 11, use OpenSUSE Tumbleweed. Mainly because that's what I use. They were with me when I set it up to choose a name for the computer, a username and a password (for their user and for the disc encryption).
I showed them how to configure wobbly windows (most important part) and how to use Discover to install games.
I installed Minecraft. I installed Steam (which has its own parental controls). I configured emails, Nextcloud and a password manager. I configured automatic updates.
I think that's about it.
They're responsible. They ask me for help if they need some. We educate them about people they meet online in Minecraft and other games. Works well so far.