I sent these as part of a Christmas gift for my 17 month old nephew & they fit him perfectly! He still wears a lot of 12 month clothes as he is really quite small for his age, but upon reading the reviews that indicated these tend to run small, I ordered the 18 month onesies and am really glad! My sister said she loves that they're bright white & he can wear them under many of his outfits for those really cold days.