I bought size 6-12 months for my 5 month old to wear this summer. It is much too big for him.  His head circumference was 16.75" at his well visit last month. My 3yo daughter tried it on and it fits her with a bit of room to spare. Actually, it looks really cute on her, so I've decided to let her keep it. I wanted to come back and order the infant 0-6 month size for my son, but they don't have that size in this design. Too bad, because I really don't care for the others. I went with another brand that fits more true to size, but doesn't have chin strap like this one.