Like others said size up. My daughter wears a size 12month. I bought the only size I could that would be here by Halloween. 12-24 month and it fit perfect, instead of being big. Also if you are looking for it with the gloves, don't bother. I got the one with gloves, I knew my daughter wouldn't wear them, but if I wanted them I'd be disappointed. The gloves fit me. Adult womens size small in a baby 12-24 month costume. Not even close. If your daughter doesn't like head bands, the crown does come off and can be Bobby pinned into hair. For Halloween and dress up it works. I didn't give it 5 stars because of the gloves, even though we didn't need them, it's just adult gloves with a baby costume.My twin girls are going to be Princess Peach and Daisy for Halloween. They are 17 mos and generally fit anything 12-18 months fine. I got a 2T based on other reviews and the length and fit are PERFECT, not too long or short with just enough extra room to slip on long sleeves in case it is chilly on Halloween! Would recommend for the good price, just size up!This costume for some reason doesn't look a lot like princess peach. I don't know if it's the neckline or what. Either way, it's cute. The quality is good and it looks more comfortable than some of those plastic like costumes. My child is 23 months and wearing 2t. I saw the reviews and ordered size 3t. The fit is good. There should be just enough room to put warmer clothes underneath. Definitely size up 1 or 2 sizes. If your child is between a 2t and 3t, maybe order a 4. Only wish this came with a crown or gloves.Super cute but does run small. Sized up to 2T for my tiny 17 month old and fits perfectly!Super cute but runs small. Make sure to size up by at least 1 full size. Maybe 2!