This was my thought as well.. Some kids stay thin, others chub up during puberty and then lose it when they stop growing like weeds.  When I was twelve or  thirteen I gained like 7 inches over one summer and I had to buy clothes that were like.. 8 sizes bigger or something . I got stretch marks from how freaking fast I grew. My hips exploded as did my chest. And the rest too, at that point. I was always hungry, but I ate healthy food, no fast food. Maybe a few too many cookies.  Once I hit 16 it started to drop off, and I dropped down in weight and size. Kept the hips and chest though, but the excess fat was nowhere to be seen. Stopped being hungry all the time  and as it is now I can't eat as much as I did when I grew even if I tried. I would probably puke halfways.  Just idk. Unless you're feeding your kid with shit, you shouldn't worry that much. Kids are just super weird and awkward.