If you make such a restriction, they'll secretly buy some cheap "unrestricted" device like some Raspberry Pi (just like earlier generations bought their secret "boob magazines").
I love gaming, but I hate all the smutt games. It discredits the medium, essentially what has also happened to anime.
I don't really want to turn on age-based filters (to the point that I've never investigated if they even exist) but at this rate, there's hardly anything worth looking at in the recent feed.
It's just hard to imagine that's anything close to what Nintendo wants users to experience, but I guess they need the money.
Your kid is screwed either way. Unless he moves to India.