My 4 1/2 year old likes cars. Real Racing is obviously out...too realistic, he'd crash really quick and get po'd. 4x4 Jam looks interesting with its open routes. Presumably he would get really far behind really quickly unless there is an easy mode or an unending amount of competition. Maybe something more in the arcade-racer genre?
Real Racing is probably the best one because of how it can handle both acceleration and braking automatically. All you need to do is tilt.
I think there is a positive and negative side to 4x4 Jam for young children. Positive: A "free roam" game mode is offered. Your son can drive around in cool offroad environments endlessly, not worrying about competition. Negative:In the other more "racing" modes (with other cars) there is no track to hold you in, so with poor steering, you could end up in the middle of nowhere. If you don't think your son would really mind not seeing many other cars on the screen, then 4x4 jam is a great choice, imo EDIT: completely forgot about Crash Kart. That one is definitely perfect for young 'uns. My five year old cousin had a blast playing that on my iPod. So this would be a great choice too. The computer players really seem to play down to your ability, and with the powerups its easier to catch up if you fall behind. Thus, my cousin was still capable of competing with the AI. So yeah, this would be a great choice too.
You may want to try a game called Phaze Racer. On the easy setting, the game is manageable using tilt and the graphics are pretty. Yes, it uses futuristic looking cars. Crash Nitro is not a bad option with its cartoony graphics, but he will fall behind easily and there are gaps in the road that can make it frustrating.
SlotZ racer could be fun, but it's a little on the hard side. You could eliminate that by playing in 4-player mode and just letting two cars sit idle. Seems that Draw Racing might be an interesting choice - I've seen 4 and 5 year olds land planes in Flight Control, why not draw to move cars around? One of my favorites, Jelly Car, is free, and while not necessarily easy, is a lot of fun, even when things go wrong! Traffic Rush is darned cute, and makes me feel like a kid, but might be too hard for one. Any interest in trains? Yardmaster, while not the best train game out there, is notable as it's got a "kids mode" where the trains don't crash...
For a kid probably Crash Kart, which (to me at least) is one of the best iPod games to date. Also I would recommend Phaze and Raging Thunder, especially RT which is very arcade style and easy but hard enough to keep you interested.
Gangstar. The game has free roam driving. Your 4-year-old will surely enjoy jacking cars, running over pedestrians, and ramming into other cars.
