I picked this because I like the colors to match the baby sister outfit I had bought. My son is a small 8 yr old and fits in small-medium size 7-8 shirts. I picked the medium because I read other reviews saying it runs small. Well the medium says 10-12 on the tag. I really wish they would of put that in for sizes instead of me guessing. I'm going to let him grow into it. That's the only reason I give it a 4. The quality of the shirt is good although he hasn't worn it yet.