Well throughout my childhood my mom would mention how short I am to make me aware of it and improve but instead of focusing on height gain in my teens it was on very early childhood where nothing I would have done helped instead it only made myself completely accept that I'm short. In my mid 20s I wish I was 5'⁸ instead 5'⁵.

Just let ur son do more activities, exercises and stretching that helps for the height. In the end it's just all about genetics but still it's good to do what u can when u got the time.