My opinion is kind of biased I guess because we have always been xbox lovers in our house lol PS3 are terrible if they plan to do any online gaming through the play station network. The built in wireless is unbelievably slow. As far as games, there aren't as many kids games available for neither xbox or playstation than there is for Wii or the handheld games like Nintendo DS. Just depends on your kids' ages though. However, we do have the Kinect for our xbox and my 4 year old absolutely LOVES it. Good way to keep her active on those rainy/snowy days. Most of the games for Kinect are also available on PS3 as well.
Just to add something about the internetnon the ps3, unlike the 360, is free to get online.I don't use any of our systems except to get on Netflix, or watch a movie. Buddy hubby pals ps3 way more than the others