Animal Crossing New Leaf is fave of dds and mine. It's never ending, based in real time so time passes in the game the same rate as real life. You're a town resident and have to talk to animals, fishing, big hunting, building stuff in the town, all sorts of stuff to do.
Mario Kart is fun. (Pretty sure I did the same a pp and threw cartridge out accidentally as it went missing Boxing Day, one hundred per cent not stolen.
Anything Mario based really we both love. Super Mario Bros, Luigis Mansion etc
Professor Layton series is another fave but might be something you can do together as the puzzles can be tricky for younger ones. I think dd was mostly ok at 8 but needed help with some of the trickier ones.
Dd also loves all Pokémon games.
Hyrule Warriors.
Pilot Wings Resort.
Anything Zelda.
Tomadachi Life
I'll go check her entire games if you like and list the most played but those are the ones off the top of my head she's played a lot.
If you do buy him one I'd recommend turning it on, setting up etc and installing any software updates before giving him on Xmas day. Some console updates can take ages and seem to take longer on Xmas day (prob everyone updating at same time lol)