Crocs are a great product...a bit pricey but lasts and is so comfortable.  However, sizing for children is a problem even if you measure their feet.  I got 2 out of 6 grandchildren's sizes right.  I even looked at the crocs.com website before I ordered.  Amazon is a very reliable site to purchase shoes....I think it could be crocs has the sizing all over the place.  Not sure.