"Order a couple of sizes larger than you usually would. My son wears a size 6/7 and I read a previous review about it running small. So, I ordered a size 8 and size 10. Couldn't even get the size 8 over his head and pants were extremely tight. We're keeping size 10, it fits ok, but if he moves his arms around a lot will probably end up ripping the seams. I should have ordered a 12, but need the costume for a school activity and don't have time to reorder."