I got this pair in Toddler Size 4 for my 15-month-old daughter and they fit her perfectly.  I was bit hesitant at first since she has never worn rain boots so I wasn't sure if she would be willing to walk in them.  Since her daycare takes the kids outside (rain or shine), she needed to have high-quality, waterproof rain boots so that her feet won't get wet.  (We live in Seattle, so chances are good that she will be out in the rain.)  Not only does she love to stomp around in these boots, they keep her feet completely dry.  Highly recommended.