This hat is so so so cute!  I purchased size 12-18 months and it fit my 11 month old perfectly.  The other review noted the hat was small.  My baby does not have a huge mellon head ... her head size is slightly smaller than the average according to her last check-up.  It probably will not fit her in 3 or 4 months from now so I would have to agree with the other review that the hat does run a tiny bit on the small size.  The quality of the hat is excellent!! It is very well made. I am very very happy with the purchase!