As others already said, Shredder's Revenge is just an amazing game. It will draw you in with the nostalgia, but also is simple enough for my 4/5 year old to crush it on his own.
There's multiple difficulty levels which really helps for the little ones. Can't recommend that game enough, especially for the price. And the length of it allows you to beat it in a few sittings which is a nice accomplishment feeling for the juniors. And i've noticed little kids aren't like us, they don't beat a game then throw it to the side. Replay value is real.
I would also second the Lego games, find the topic your little guy really likes then run with that. For me it was Harry Potter. They can usually be found for a steal on sale as well, I think we got the complete collection for like 85% off. Just be prepared to carry the game play as there are a lot of puzzles, but also if you have time/patience it's great to work through some of the easier ones with the little kids. It also helps to keep a play through up on your phone while you play
Funny thing is, that was actually my kids suggestion as we struggled with where to go at one point. I remember having access GameFaqs by the time I was about 13.. but this new generation definitely has more resources for h4x.