Place a piece of paper on a hard floor against a wall
Have the child stand on the paper with heel touching the wall
Make sure the child is standing straight and putting full weight on the foot
Mark the longest toe on the paper
Measure the distance from the wall to the toe mark in inches or centimeters
Measure both feet and use the larger measurement
Compare the measurement to a kids shoe size chart
Add a little growing room if needed, based on the shoe style and brand
Check the fit by making sure there is space at the toe and the heel feels secure