12 year old son appears to be getting a little chubby. When to worry?

I have noticed that my 12 year old son appears to be gaining some weight around his mid section. He is an athlete and is very active. He plays football in the fall (linebacker and fullback, so lots of running around) and baseball in the spring (catcher, so less running). He's also always out riding bikes, climbing trees, and playing sports with the neighbors.We have healthy dinners, but he does tend to snack a little during the day. We do have plenty of healthy snacks that he eats, but he also eats some junk food. Should we start getting stricter about junk food?I know that girls generally start to gain some weight around puberty, but I haven't seen the same thing happen to males. I (male) have always been very slender. My oldest son (13) has also always been skinny as a rail. Oddly enough, he doesn't play any sports and eats worse than my younger son.Should we be worried about some genetic issue here? Because he is already very active, is there anything we can/should do to help him with his weight? Anyway to do that without making him insecure?If it matters, he is pretty short. He's about 4'7 or so. Is it possible that this is just a growth spurt? He still doesn't appear to be showing many signs of puberty. We do plan on asking his pediatrician, but we were going to wait until his yearly physical. via /r/Parenting http://ift.tt/2oSILpn