Pectus excavatum, as you now know, is when the breastbone (sternum) dips into the chest. Generally, this is not a medical problem although it can be cosmetically unappealing.
Whenever a child is diagnosed with pectus excavatum, the most important thing to do is make sure that there is no evidence of a connective tissue disorder, like Marfan's disease, as there is sometimes an association between pectus excavatum and connective tissue disorders. Presumably your child's pediatrician
has already taken a good family history and performed a good physical examination and taken care of this.
Assuming this is isolated pectus excavatum, without any underlying medical problem, then there is no need to do anything. As your child grows, the pectus excavatum will often become less prominent. There is a surgical procedure that can be used to repair pectus excavatum, but it is a major surgery
that involves breaking and cutting the breast bone. It is best to avoid this surgery unless there are medical problems from the pectus excavatum (which only occur in very severe cases) of if condition is extremely cosmetically disfiguring.
If you have more questions about this issue, don't hesitate to talk with your child's pediatrician again.