True to size, I've found, in the smaller sizes (no experience with larger sizes yet!). DS just turned 4 but is petite (38" and 30-ish lbs) and is just sizing out of the size 2/3 and into the 3/4. I love Mini Boden, right up there with Hanna Andersson and Tea Collection for kids wear: high quality fabrics, hold up to a lot of abuse, and really adorable designs. Mini Boden is my go-to for socks, undies, and swim trunks in particular (love the shorty swim trunks they do for boys -- so much better for swim lessons than the big baggy ones).