1. Kirby Air Ride--Kirby rides around on a selection of cars that coast, fly, and swim. In free play mode, you can explore all day without worrying about completing tasks or running out of time. On the competitive selections, it is sooooo easy to lose on purpose, ensuring smiles and a sunny disposition the rest of the day. (Unless you are philosophically oposed to letting him win, in which case, feel free to win, win, win.)
2. Mario Party Seven--Following a board game format with minigame options, a round of this can fill an afternoon. It includes 4 players, regardless of the number of humans actually participating. Therefore, you have some free time to check email, make short phone calls, or shop on line while the CPUs take their turns (Warning--you will miss some of the fun that way). You can "cheat to lose" on the minigames, but not the board game portion. Great compromise--play the minigame portion, so Junior can win all day!
3. Animal Crossing--A sweet little game that allows a childlike character to buy a house, get a job, pay a mortgage-- and somehow the little ones think this is great fun! Mom can sign up for her own residence, and play along, allowing her to funnel earned income to the child. Junior can then continue shopping, designing clothes, fishing or otherwise having fun without actually having to work for a living!
It's really great how the older ones can enjoy the same games without the parental support, by playing as they were intended to be played!