Pectus excavatum is when the the chest indents rather than having a nice curve. If the pectus is not severe, then there should be no compression of the heart or lungs. Without compression of the heart or lungs, the pectus excavatum does not need to be repaired.
If the pectus excavatum does cause compression of the heart of lungs, a parent should look for shortness of breath that is increased from other kids of the same age or chest pain. If your child does have these symptoms, see your pediatrician about referral to a surgeon. When seeing a surgeon, they will have to do a CT scan of the chest in order to take measurements before a surgical repair can be done.