Turbo Boys' Poo Emoji Swim Brief Swimsuit

This is a fabulous bathing suit, I wish I can wear this yellow poo emoji swim brief, sadly, I can't, however, I have seen a former neighbor wear this bathing suit and he loves it!!

My son is a big 6 year old. (He looks 8) I ordered the largest size 5T and hoped for the best. What came was a suit with a tag that said size 30. It was enormous, and would never fit a 5 year old. I was able to exchange for a 4... but it was still too big. He wears it only at home now, because I couldn't be bothered with another exchange. I'm not sure if the T means it fits over a diaper or something? The leg holes are way too big.