I bought the medium one (which said 12-18 months) but when I received the suit the packaging said 6 months to 2 years. It's really big - it definitely fits a 2-year-old's size; I have never met a 6 month old (or 12 month old) that would fit. The head piece fits without problems, but the main part is too big; I'll probably have to get another suit for this year and save it for next year. This is a lightweight suit, you will need to wear clothing underneath if it is chilly outside. And the brown part of the body looked almost metallic. It's really cute though!