My review has similar comments in respect to needing to order a size up. I own a pair of lined crocs myself and needed to do the same thing. My daughters is nearly 39 months and her foot is currently a 10. I order the 10/11 and 12/13 shoe just to see for myself. I kept the 12/13 shoe. I bought them as easy slip-on shoes during the winter months (house to car/car to daycare),  nearly 3 months from now. The comments about lack of breathability didn't matter to me so much because she's not going to be wearing them for hours; even so, my daughter wears 100% cotton socks, we use shoe powder and the lining is washable. My concern was that snow/moisture wouldn't get into her shoe. The lining, lines the perimeter of the shoe and sits well into the shoe; however the strap rests 1/2&#34; (about a thumbnail) forward from the back of the shoe; therefore pushing the foot forward. I took the lining out of the shoe and to see where my daughters foot sat in it; she had about a 1/2&#34; from the front of the lining left, so essentially that meant that when my child's foot was in the lined shoe, the lining would be snug like a sock and her big toe would be the touching the shoe gently (just like what occurred in my own crocs), which I think is uncomfortable. With this, I found it be best to keep the larger size. She does like them and wants to wear them in the house now. She does not have any problem walking in them with or without the strap.  By the end of winter, she'll probably be a size 11, and she could continue to wear these in the spring if she wants. Since the shoe is a 12/13, they might serve a third time without the lining in a future summer season.