My skinny son 7 (+11 months) years old. 47 pounds, 50 inches tall. I have the small one and it fits him perfectly. It hugs his chest, which is quite thin. The velcro is not strong so pulling it forward will release the back opening. I will only attach pins or stronger velcro. He likes the costume, the mask is made of plastic. Overall not bad. I assume it will last through the season.