I have here a Buell RB2 wetsuit. It is a size Junior 14. It is a H5/4/3mm, I don't know for sure but I think the hood is 3mm and the body is 5, and the arms are 4. It is a heater of a wetsuit. My son probably wore it 4 times.
kids shapes are so variable and wetsuit sizes are hard to figure out per brand. I don't know how tall he was when this fit him well and he was a thick child so we had to get it a bit too large for his hight. Best advice for fitting is to go to a shop that sells this brand and try one on or do a best guess and you can try it on over some board shorts or something. It is clean and doesn't smell. washed with proper wetsuit detergent.