I don't have any children, so I'm just throwing a few ideas out there, but others might be able to add more feedback:
-I think Mario Odyssey might be a good one, because there's the assist mode that removes any penalty from dying, tells you where to go, there's a ton of stars that are easy, and as a last resort there's the two-player option so he could control the hat and you could control Mario.
-Snipperclips might be good if you plan on playing with him as well, but you'd most likely have to direct "okay, now turn to the side, cut my shape" etc. That one has a bit of a cutesy aesthetic that might appeal.
-I would assume he's probably not ready for Minecraft yet, but I know people use that one for educational purposes even.
-And then I'd also say the Lego games are supposed to be really good for families too.