I'm going with Deb. For BMX, yes, you want a little 'squish' so you can get a good grip on the surface, but you need to also have sufficient air pressure to prevent pinchflats. Have him check his tubes for ol' snake bites and if he's got 'em, up the air pressure. Might be harder to do some tricks (less squish) but that just means more skill is needed. Oh, and don't let him beat me for that last sentence.