

I used to always use Minecraft for this. Sure, they can’t do everything immediately, but I put the game on peaceful and let them explore at their own pace.
I say “used to” because Luanti (formerly MineTest, an open source Minecraft Clone*) is finished and free.
(Okay, Luanti is a lot more than a Minecraft clone. But for this discussion that’s all one needs to know.)
My best guess would be some relatively passive notification stealing focus.
As reddeadhead mentioned, there’s specific “don’t steal focus” settings. I’ve had good luck with them.