Atlantis Shoes should fit snug as they will stretch. Please follow our size chart to find your matching size. It is important to measure your foot on a flat surface with your heel against a wall or straight edge. Use a ruler to measure the length in millimeters or inches from the tip of your longest toe to your heel. Keep in mind that your longest toe isn't necessarily your big toe! Measuring your kids foot can be tricky :) please try to measure your child's foot from heel to big toe and pair it with the equivalent Atlantis Kids Size. If you are between sizes we recommend going with the smaller one. Learn More.