Well, is the PS3 price enough to put you off? Because we don't know when the price cut will happen, and you plan to get a console in the next few weeks. You do get a lot of extra multimedia features with it, and online play is free.
In defense of the x360, if you get one it'll be a Jasper so it runs pretty cool. Mine is one of the last Falcons made and it seems fine enough without buying extra coolers. I haven't bought any accessories for it either, all you need are some rechargeable batteries, most households already have those anyway (you would need that for the Wii too, or buy an extra recharger).
For the Wii this year looks good too, people already said enough about it as a choice. My niece is 3 y/o and enjoys it a lot when they visit, so your kid is not that far off :)