Ooh that sounds great! My boyfriend and I are lucky enough to have found each other as co-op partners for life. We are trying to teach our little nephew a thing or two though. He's about 3,5 years old now and he's not great the the finer things yet, but he does enjoy playing some Pokemon Rumble World on my 3DS ;-)
A Wii definitely sounds like a good console for a young one, though I have to admit I don't know much about console gaming anymore. I used to love Mario Kart, Super Smash and Snowboard Kids when I was little. That was back when we had a Nintendo 64 :D
Console gaming for me is optimal, since it allows room for the both of us to sit in front of the TV. Computers would be a lot more difficult (since I'd need two). Nintendo games do tend to cater more for younger gamers, but as said, I have some nice games on the xbox that work perfectly.
I'm sure you're 3.5 yo nephew will get better over time ;)
Yeah, with a little one I think a console works better indeed :D