My son is on the (very) slim side and we struggle to find jammers that are long enough with a small enough waist.
I ordered these in a 22 (he's nearly 9 and 134cm tall) and they fit like a dream, they also still come down to nearly knee length whereas other brands look a bit too short on him.
Postage was quick and well packaged, I’d definitely use aqua swim supplies again when we next need jammers - I’ve been told that I’m not allowed to buy anything other than funky trunks now (!)