Do you know what kind of games they would enjoy?
Like someone said, the Wii, while I think laughed at by more hardcore gamers, might be fun for them to play and the titles aren't really as intense as the ones available for PS3 or the 360. Me personally, will probably look at the Wii if they put out a good Star Wars game for it. The controller would be great for some lightsaber action :woot2:
The 360, right now, is the most popular system and has the larger video game library at the moment. That is, 360 original titles. If you count backward compatibility, the PS3 probably would get that medal.
Multiplayer is a big thing now. It wasn't when I was gaming, and I really don't care too much to play online. That being said, they might want to play their friends or other people on XBOX Live. Now, this is where a lot of crap comes into play. It varies from game to game, but they can be verbally assaulted from racial epitaphs, sexist crap, to being exposed to nudity. That seems to be a favorite when playing Uno online. I don't know why...
Will they be exposed to anything that they wouldn't be on the schoolyard? I doubt it. But just so you know what is going on online so their parents won't go off on ya.
Then there's the way Microsoft nickel and dime you for just about every little thing on their online service.
This is where they make their money. Microsoft knows who their target audience is, so if they have disposable cash. They'll be throwing a lot of it away.

Also, once you enter your credit card info to buy anything online, you can't delete it. They have it for life. I still don't understand that. I pick up a pre-paid card at a local GameStop and use that to buy anything that I'd want to get so I don't have to add my CC number.
As mentioned, people have been experiencing many problems with their 360's. But I don't know if it's just a case of the person who yells the loudest, but it seems like there might be a widespread problem that seems to be from overheating, but there could be other issues as well. Some people's machines failed when turning them on after having just received their "fixed" machine.
I'm a casual gamer and don't really play it much and not for hours on end when I do, so mine might not get as abused as others. It's also well ventilated. Also, customer service seems to be a nightmare.
Having said all that, I still enjoy my 360 and have been fortunate to not experience any mechanical problems. I'm not up too much on the PS3. I know spec wise, I believe it's the better machine, but a system is only as good as the games for it. But I hear that next year might be their year. Didn't hear any specific detail as to why, however. But I don't think it'll make people shun their 360's. The PS3 just needs more popular titles. What I've seen doesn't really move me, personally. And that price tag is out of my reach.