COD online can be as quick as you like. I sometimes drop in for about 10 minutes because I have to admin the server (kick out problem players). I can jump in, shoot a few people, watch for idiots and get back out. My son started playing it when he was 8 so even kids can pick it up.
The sniper servers are very slow-paced which can be a welcome relief. I wish I had it when my kids were really young. When my daughter was 2, she would sit on my lap and watch me play Harpoon, yelling “BANGO” everytime a missile hit a ship.
Things have changed since my old Atari 2600. Back in the day, I didn't need to use my Engineering degree to play a ##$%$#%! video game. I hear that the Nintendo Wii is pretty easy to use, though. I might look into it when the kids are old enough.