My daughter is 16 months old and has an average-sized head.  I ordered the Retro Banz in the size for 0-24 months.  The frame of the glasses fits her face just fine and looks good, but the neoprene (reminds me of wetsuit material, so it'll probably float the glasses up if they fall off in a pool) goes right over her ears so it looks odd, pressing her ears against the side of her head.  We've also tried putting the side straps over her ears the way regular glasses are worn, but the straps are so thick that they come down and fold the top half of her ear(s) down.  I can't figure out how to position it so it doesn't do that.  We've tried pulling the back of the band high up on her head, and tried lowering it to below her skull above her neck.  Putting it above makes the glasses easy to fall off, but the straps really aren't long enough to have it sit underneath her skull, and plus that latter position pulls the top soft cartilage of her ears down again.  Speaking of the straps not being long enough, we've got the velcro adjusted to as far out as it will go to still hang on, and the glasses frame still leaves a deep groove between her eyebrows and two smaller grooves from the nose pieces on either side of her nose under her eyes.