To determine if a child's shoes need to be replaced due to wear, you need to check the following:
Bottom sole. Look for excess wear on the bottom sole, especially if your child's feet have a tendency to pronate (roll to the inside) or supinate (roll to the outside), which will cause one side to wear more than the other. Dr. Carol Frey, Assistant Professor of Orthopaedic Surgery at UCLA and Chief of Foot and Ankle Surgery at West Coast Sports Performance in Manhattan Beach, California, recommends placing your child's shoes on a flat surface and looking at them from behind. If they roll in or out too much, they are probably worn out. Wear patterns can also be helpful in evaluating an athletes' biomechanics and what shoes may work best for them, says Dr. Phyllis Ragley, past President of the American Academy of Podiatric Sports Medicine ("AAPSM"). Shoes can also become slick and lose traction when the soles and lugs are worn down, so that is something else to keep an eye on.
Mid-sole. According to Dr. Michael Lowe, past President of the AAPSM, shoe wear should not be evaluated primarily by sole wear. The most important wear factor for a running shoe or court shoe, says Lowe, is compression fatigue of the mid-sole material (the material between the sole and the upper leather). Like any compressible material, it has a certain life expectancy, after which fatigue begins to lessen its efficiency and ability to decrease impact forces. Putting athletic shoes on a replacement schedule is recommended.
Sock liner. Check the inside liner of the shoes for areas which may be worn through. This may provide information about places where the shoe was causing excess friction on the child's foot. Be aware of those problem areas when purchasing new shoes.
If after numerous washes the smell just will not disappear, it is time to throw them away.