I am writing this review so others know what size they may get. A Medium was 6 - 12 months. A Large was 12 - 18 months.I ordered medium and large hoping one would fit my 3 year old toddler who wears a size 9 shoe. Of course, these were both way too small! However, they do look really cute in person. I wish they sold her size.Was looking for something that would stay on my daughter's feet and keep them warm. I was a little disappointed that the elastic at the top was not as tight as I thought it would be.My tall, thin 11 month old's foot is 4.75" long and the 18-24 month size fit PERFECTLY. The quality of these slippers is good for $10. I bought them for her to wear in the mornings when we head out to drop off my kindergartener and to wear in the BOB stroller on our walks (with the urban bundleme on colder days) and these will work perfectly.I ordered size 12-18 months and it is EXTREMELY small. On their label it says up to 12,5 cm. But in reality is is just above 11cm. Also incomparison to Carters size 3 it is very small. Another big thing is that they claim the sides are made from leather. It is NOT. If you look closely, You can see that the reverse side is man made. Very dissapointing. I gave a second star for the nice design and idea.My baby is small for his size and the 6-12 months were so small he couldn't get his foot in, and he was 9 months old. I returned and ordered a size up and it unraveled and fell apart in a number of days. I returned and am waiting on a new pair. I hope the fact that it fell apart so easily was a fluke and that this new pair holds up, as they seem quite comfy and cute, and match most of my son's outfits.We ordered these last winter for our 1 year old twins and they wore them all season and loved them. They weren't able to pull them off because they go up the calf a bit more than the picture shows. We ordered them in the larger size (18-24) based on the reviews and didn't have any issues with them being too small. I just pulled them out again they are still in good shape but one of my daughters feet are now a 6.5 and they are too small. Quality was great and we didn't have any issues with them slipping.Got these for my niece who is 1. They are so cute!My friend gave me these in the 0-6 size for my babyshower. They only fit my daughter for a month because, like other reviewers stated, they run very small. They are such high quality for the price though, and so cute, which is why I give them 5 stars.The inside of the booties look like the inside of a sock. So, so soft! I didn't have to worry she'd get her feet tangled in threads or poked by tags like other cheaply made booties. She's a big girl, so I'm going to buy the 12-18 months size, even though she's only 3.5 months :)