It's so difficult to know to be honest, my baby fits them on the smallest waist setting so no doubt they'd be fine for little thighs but its just the length with her being tall. I went up to the large and used a wrap as the large were a bit big overall and gaped a bit at the leg gussets so again, if your lo has chubby thighs may get away with a large? If its a little on the big side they are still really trim under a wrap if you have any, I also have a couple of flip wraps I'm selling if you thought that might be an option and need wraps, until she grows a bit into them. Hope that helps a little bit

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