Size down one size.  Otherwise, this romper is adorable!! Thick and well made.  If you purchase to fit, size down one. I purchased our size knowing it would be a bit big but I wanted my son to be able to wear as knicker/overalls and criss crossed the straps in back before bringing forward to button. I purchased at his 1st bday (19 lbs) and he will be able to wear them again this late fall and winter on the last button. I would pair with some wool leggies and leather boots for a perfect vintage look. Purchased in 2 colours and will purchase again.