I make these fleece hats to fit infants to adults and everyone in-between. They are warm, soft and hug the ears. Even without a strap they stay on a babies head.
XSmall- fits 14-16 in. (infant 0-6m)
Small- fits 16-18 in. (baby 6-18m)
Medium- fits 18-20 in. (toddler 18m-5T)
Large-fits 20-22 in. (kid, 6-10)
XLarge - 22-24 in. (teen and adult woman)
XXLarge 24+ in. (adult man)