To determine size please measure the foot from heel to big toes in centimeters. To your measurement add 1.5-2 cm for sufficient wiggle room and use that number to choose the correct insole length.
**When in Doubt Size UP**
For Example: Babies foot measures 12cm. Add 1.5-2 cm to get ~14cm. You would use the size chart and pick a SIZE 5/6 based on the insole measurement . Remember the soft sole will mold the foot and allow the baby/child to grow into them giving you more use out of your Huddy Buddies
Simply place the foot onto a piece of paper and draw a line at the heel and then at the big toe. Measure this distance with a measuring tape or ruler in centimeters and use this number to choose your size.