I bought the KidZ BanZ (as opposed to the Baby BanZ) two months ago for my then 9-month-old because he's in the 97th percentile and at the time was wearing size 12-18 month hats.  These sunglasses fit great and I'm SO glad I bought the larger size!  They are very adjustable and he should get a couple of years of wear out of them.  The baby size would have been way too small.  My son doesn't mind wearing them and doesn't try to take them off which is great.  Plus he looks adorable.  :)