If you mean pure desktop, probably whatever age you’d need to be to use windows. Switching from Windows to Linux is an adjustment for most normal people, but a big part of that is because they’ve been using windows for years and are used to their design choices. At the end of the day, though, in either case, shortcuts on a screen are shortcuts on a screen, and you’re not going to be ready to manage either OS for a good while.
In terms of using it as a handheld, the flow is pretty easy, but it’s really big and heavy for a little kid.
One other suggestion for game mode with kids: you can use decky loader with the CSS Loader plugin to customize the experience and remove elements that you don’t think are needed. I’m not sure if you can straight up hide the store completely or not, but you can definitely hide the news and other tabs that might have content you’re unsure of.
