... I think he is verging on overweight.
He is huge anyway - 98th percentile for height, size of average 9yo - but he seems to have larded on a bit over the holidays - is weight of average 10.5yo, particularly hefty around the tummy.
He's not exactly sporty, but very strong & has masses of stamina - can manage eg a 4km run or a 400 metres swim, happy to do long walks & would surf all day if allowed. So not a slob. He doesn't eat between meals, never has; but eats huge amounts at every meal, which is always proper food but does include a biscuit here and there. (He doesn't eat anywhere near enough rubbish for that to be the culprit, and we switched from full-fat to semi-skimmed milk a year or so ago.)
I know I should take gp's advice, but does anyone have a child like this or know what the current thinking is - should I intervene? - eg not let him have second helpings, do more protein/less starch, make him run about even more?