Do not get overly scared. A heart murmur is present in many people and often without any complications throughout their whole life.
Murmur comes from an abnormal blood flow in the heart.
An innocent murmur can be heard from a fast blood flow (from exercising, fever, anemia etc).
An abnormal murmur can be heard from i.e. valve abnormalities. In these cases the blood flows in abnormal directions or with abnormal speed, causing the murmur sounds.
Often, even abnormal murmurs do not progress and require no treatment at all. Some more severe cases are monitored only (an echo once/ 2 years) and in very severe cases treatment might be necessary.
Valve abnormalities and other heart abnormalities that cause murmur can be congenital, so yes, it is possible that your son's murmur has the same cause.
With a stethoscope, a murmur can be easily heard, and a cardiologist can probably in many cases already pinpoint the cause, but the best way to find the cause and the extend is with an echo.
Many people have murmurs and never know it until a routine check up. They never have problems. Other people do have dizziness, fainting spells, shortness of breath due to temporary low oxygen being circulated (skipping beats) For the same reason it can cause chest pain. It depends on the cause of the murmur from nothing serious to a hole that didnt close at birth or incompetent or diseased valve . i would definitely take her to the cardiologist and find out