UPDATE: I finally got around to installing the Hutchinson heavy duty tubes I bought a while back, and the back tire was flat within 10 minutes of riding. I'm starting to think the problem may be with the tires, which look a little weather worn even though the bike is only a year old. I inflated the tires to the max on the sidewall - 40 psi - and they held air great until he tried to ride the bike, then it's no go pretty quick. I'm thinking about buying some Maxxis Hookworm BMX tires for about $21 each, which can go to 110 psi and trying those - do you think that would do it, or could the problem be the wheel itself? By the way, this is a pretty cheap Razor bicycle ($120), but it seems pretty solidly built, not sure about the wheels though. Any help=thanks mucho!!