My DS10 has always been tiny, very slim and very short he is still at least a foot shorter than anyone in his class at school.
I have suddenly noticed that he has a bit of a tummy and some moobs 
He swims once a week, we have a trampoline but have had it for a few years so getting him on it is a task in itself, he's bored of it. He loves to ride his bike but we are in a built up area of Birmingham and on a busy bus route, so I only allow him out when I am free to stand out with him.
His diet is pretty good, mostly home cooked meals, with an appropriate portion - although he is always hungry and will moan I haven't given him enough ...
I just wondered if it was finally a growth spurt but I don't think it is.