Here's an easy way to determine the shoe size of your child.
Using a measuring tape, measure the bottom of the foot from heal to big toe in inches.
As a starting point, 6 inches = size 10.
Each 1/2 inch is 1 shoe size up or down.
Once you hit size 14, that is youth size 1.
Example,
Measure 4 inches = child's size 6
Measure 8 inches = youth size 1.
Let me know if you have questions.