Wow, what great suggestions you have gotten. We are big into games at our house. Ours are 3 years apart and DD just turned 2, so generally we have been playing more games with DS when DD goes to sleep since he plays adult games mostly anyhow. We already do a bunch that were mentioned so I don't have too many more to add. But we do have a few that I could see would be adaptable that I don't think others mentioned:

Apples to apples jr.
Pass the pigs
Izzo (puzzle)
dominoes
don't break the ice
mouse trap
cadoo
bingo
sorry
card games: old maid, go fish, rummy, blink, etc.

I also like the mindware stuff. I think Qwirkle sounds great. DS turns 5 next month and I didn't get it for him because I already got him so many other games.