Why would my Can-Am DS 90 backfire, it's brand new?

I bought a 2008 DS90 X Package 2 days ago, and when we got it, it ran really good. It was parked and ridden a few times since then and it wasn't ridden hard at all. It was a little kid on it (my 7 year-old brother) and it is sputtering and backfiring and acting up. He put it up until tommarow, but instead of taking it to the shop, is it something easy to fix or should the warranty cover it? I think it is a foweled plug or something. Give me some possibilities, thanks :).