"My son is an average sized one year old. His everyday clothes are between a 12 month, and every once in a while an 18 month. I ordered the dino shirt in the 18 month. It is so tight on him that I am afraid to wash it before his party. I have now paid 15.00 for a shirt he will probably only be able to use once. The other items I ordered were wonderful. The shirt sizing is simply not accurate."