I'm not a gamer but a while ago I got a powkiddy v90 after asking a similar question it was recommended. I agonized over it and did some reading about different systems but in the end I didn't find anything better. Well actually a device called Miyoo Mini at a similar price was universally reviewed as somewhat superior specs-wise, but it is too small it looked uncomfortable to use so I didn't want it. But if you don't think you will get cramped hands maybe consider it.

After that there is a big jump in price and of course things get better from there; but I wasn't interested in spending hundreds or thousands. Only tens.

For the v90: The default interface is really confusing. I was glad the first thing I did was clone the sd card because the second thing I did was accidentally delete a bunch of stuff by pressing the wrong button in the interface after booting it up. It's hard to find things in there. The main games I want to play are mario and either they aren't included or I can't find them. I'm sure children would figure it out in no time but adults may struggle like me.

There is widespread support for using an alternative ROM, and for beginners it's the Miyoo ROM actually. I ran into some technical issues so I didn't get it done yet. (They are my own issues on my computer nothing to do with the ROM or the device.) I have high hope that one I get some time to return to this it will be muchly improved.

Prior to looking into this I got one of the $10 ali express devices that can't be customized at all and I really liked it. Only problem was you can't save your game progress so eventually it got boring starting from the beginning every time.

In terms of family which you mention, when I was doing research I came across some people making a really interesting/funny point: an offline gaming device is a way of shielding children from social media. You are giving them a screen to use but it's one that prevents all the creepy/toxic shit found on the platforms. In a way it is extremely constrained. I found this to be pretty compelling.