Hello micrho,
the easiest way to share your apps with your son is the Family sharing.
You can constitute Family sharing on your iPhone!
Just go in your Settings to iCloud and there you will see a family sharing button.
After the constitution your son will have access to your bought apps in the app store.
He just has to go to Updates and then check out the purchases - there he can download all the apps you've ever loaded.
There's also another way:
You take his iPhone, log-in in his app store (Highlights and scroll down to Apple-ID), then download all the apps and then you can logout there again.
I hope I could help you.
Have a nice day!