For my 5 year old boy...

[nintendodork]

Started him on Kirby Nes today since I remember that being pretty easy. He's having a blast. I was never a huge Kirby fan, but I can see now that he's going to have Kirby nostalgia in his 30s...

This reminded me, have you ever thought of Kirby Tilt & Tumble on the Game Boy Color? Almost the entire game is controlled by just moving the Game Boy around.

Edit* Also, back on the Pokemon thing, I myself feel like a little kid who can't read, as I'm currently playing through Pokemon Green (which is all in Japanese). Granted, I've played Pokemon so much I don't need to read much to know what anything is, but when I'm too lazy to look up online what something means, trial and error teaches me just as well. I like what you're doing with it though. You'll have trouble getting him away from his Game Boy once he can read and play all by himself.

[L___E___T]

Rythum Tengoku / Paradise / Heaven on GBA, DS or Wii when it comes.  Good for dexterity right?

 ~ and Hogan's Alley of course!  OK it's a gun game (you may have a policy), but kids do love toy guns and this one has a built-in morals feature!

[FamicomRetroGamer]

The Simpsons Arcade.

On Xbox LIVE it costs 800 MSPs, dunno about on PSN, maybe $10.

[michaelthegreat]

Thanks for so many ideas!

Manuel: You will not regret Pokonyan. My boy learned to jump and move right in that game, and He's just now exploring the upper parts of the levels. Every boss can be beaten by standing to the edge and jumping over and over again, but a kid can develop better stratagies as he gets better. Very varried levels, some with interactive set pieces. I haven't even shown him how to shapeshift yet. I wish the gameboy one looked as interesting.

Tilt and rumble does sound cool, but the controls would be backwards on a gba so I'm not sure about it till I find a gbc. I have to say, I think I need to make a video of myself playing tilt and rumble with a gamecube with gb player--too awesome!

[manuel]

I got Pokonyan today and my wife was reminded of her childhood by the cute label art.
Now I only need to find and hook up that AV multi box (now where did I put that again...), because my TV doesn't have any free connectors...

[Parodius Duh]

my buddy and his 5 year old son have been enjoying the super monkey ball and boom blox games for the wii, theres enough levels for a young child to figure out on his own, as well as harder ones that an adult can beat.

Noobow varies, I just picked a copy up for cheap after a long wait, but Ive also seen it go as high as $35 cart only....ebay price 

[L___E___T]

I've got that tilt 'n' tumble game - all the commands are reversed when I play it on my GBA SP!

[Jedi Master Baiter]

I think I need to make a video of myself playing tilt and rumble with a gamecube with gb player--too awesome!

http://www.youtube.com/watch?v=vBhJvnERukE

[nintendodork]

Tilt and rumble does sound cool, but the controls would be backwards on a gba so I'm not sure about it till I find a gbc.

I assume you mean GBA SP? The GBA would still the same as the GBC, since the cartridge still goes in upright.

[Phosphora]

I got my NES when I was just 4 years old in 1987 and absolutely loved Super Mario Bros. I'd say just get him an NES and any non-RPG games. I loved an easy 80% of the NES software library as a kid.  
If you're willing to sit down and play with him, so many of the multi-player Co-op games were epic. My dad was a big gamer in the 80s, and I enjoyed that aspect of him.

[jpx72]

Give SONIC to children! Any SONIC! WAAAAAAAAAAAAa
...Sonic games on Megadrive influenced my whole life (played since 12y)

[FamicomRetroGamer]

Since you don't have an Xbox 360 you can't experience the awesomeness of Trials HD or Trials Evolution (Released just yesterday!) so alternatively and free, RedLynx has released a free version for PC users.

http://games.softpedia.com/dyn-postdownload.php?p=78255&t=4&i=1

Edit: Sonic 4 Episode __ are total crap, so stick with Sonic Generations which is way better and the Sonic game Sega should've have had done years ago instead of Sonic Unleashed or Sonic 2006 (shit).

SU's great but the night stages kill it for me.

[nintendodork]

I'm sure MTG's son would settle for less than the current generation.

[FamicomRetroGamer]

I'm sure MTG's son would settle for less than the current generation.

Trials Legends' could be considered pretty outdated.

Though, I wish RedLynx would've released Trials Legends on Xbox LIVE Arcade too, it's nowhere near as good as Trials HD or Trials Evolution but it's still playable.

[michaelthegreat]

HA HA HA. That video made my day! Thanks Jedi... The bongos for A button are too much.  That would make an awesome gamecenter episode.

Yeah, I meant I have a gba sp for my son, sorry for the confusion there. I'm going to look for a cheap kirboy pinball cart to see if I can mod the sensor.

Thanks for the mass of ideas guys! I'm getting him warioland 2 and 3 now and will start looking for some of the other suggestions!