The answer to your question depends on what your child is going to the pediatric orthopedist for. Since you are asking about prescription inserts, then I'm assuming that you have an appointment with this orthopedist because your child is having pain in his or her feet. If this is the case, then prescription inserts can be very helpful, depending on the cause of the pain.
If your child has problems with the arches of his or her feet, then inserts can be very helpful. Prescription inserts are made of either a tough leather material or a rigid plastic. They are made to fit a plaster mold of the feet to make sure they are as comfortable as possible. I don't think I have ever heard of these types of inserts cutting anyone's feet. In addition, a soft foam would not do anything for arch support in a person with flat feet. If your child's arches are fine, then prescription inserts will not help their foot pain
If you do end up needing foot inserts, then I would suggest scheduling an appointment with a podiatrist
. This is basically a specialist that knows feet inside and out. They will be able to help custom fit inserts for your child that will change as their feet grow. Good luck.