I followed the size guide and my son normally wears a 7 to 7.5 toddler shoe.  The size guide stated to buy a 7, which made sense because most crocs run big, but these didn't.  I exchanged the 7 for an 8 and they fit great.  There is only a slight change in color when it's cold.  My son hasn't noticed it but I do.  He loves wearing them.