Good morning, my son is 13 and small. he has not hit puberty. would getting him a personal trainer benefit him or stunt his growth?

Depends: If he is being followed by a pediatrician I am sure he is on the normal growth charts. Is he below normal on the chart? At the Children's Hospital of Philadelphia they have a Growth unit where they do evaluation and treatment. There are hormonal causes for short stature. Their number is 215-590-3174 Exercise is always a good thing. It will not stunt his growth.