"My son is a size 7 and I purchased the 8-10 with the idea he would be wearing pants, shirt & jacket underneath. However, this costume is very big on him and I should have gone with his normal size since it stretches. My son really likes this costume especialy the jet pack which is sold separately. The only real complaint I have is the helmet. I tried it on and it is very difficult to see out of. I think any child trick or treating at night will have a very difficult time seeing with this on."