I have all three of the consoles that have been mentioned below.
I am an avid Xbox 360 fan and will not have a bad word said about it. I have a 3 year old that loves the Kinect, I have a a 11 and 14 year old that also love the Xbox and Kinect.
The PS3 is a very good console but as someone mentioned earlier it is aimed more at the older gaming generation although there is a good selection of kids games like Little Big Planet. The Playstation Move is ok, a little dated compared to the Kinect. My PS3 is sadly just a gloryfied media player.
The Wii unfortunately once was a good console for its original concept but
sadly now gathers dust.
Just to throw another spanner in the works for you in October Nintendo are releasing the Wii U the second generation Wii console which is gonna put them right back in the market. If this is gonna be a Christmas present hang fire and watch for the Wii U adverts, I am sure they will want one.
If it is for now then I will say Xbox all the way. Sorry to all PS3 users but this is personal preference