These little jeans were an Xmas gift for my grandson. He's 3 and 1/2 and very thin in build, of average height and dislikes pants with zippers, buttons, etc. I actually ordered the jeans in a size 4 and returned them, as I was sure they would be too small. Usually I'm pretty accurate when ordering clothing from Amazon, but had some difficulty this holiday season.Anyway, after obtaining hands-on measurements of my grandson, I purchased the same size once again and held my breath until the gift was opened. The fit was just right, with a small amount of extra room for growth in both length and width. I think if I had to do it over again, I'd probably go with a size 5, as that would ensure the jeans could be worn for an adequate time span.These are awfully cute pants and a good choice for an extra-slim fit...