I ordered the size s (4-6) for my 3 year old daughter based off the sizing chart and it is too small. Out of the package it looks like it could fit an American Girl doll. It does stretch but not enough. Consider sizing up one or two sizes.
I bought this leotard for my daughter who is 5. I didn't measure her prior to ordering, but she is average height and smaller than average for weight. I ordered the Intermediate size and it fits her now but I think she will grow out of it faster than I had anticipated. Also, the front panel doesn't have any lining, so I worry that it may not be as durable as others we have purchased. But the style is very cute and the material is very soft. I like it overall but wish I would have ordered a size larger.
My daughter fit the measurements given for the Intermediate size, and the leotard fits absolutely perfectly. The skirt is a bit longer than on many dace leotards and I appreciate the option to have my six year old in something a tad more conservative.