How to stop my text messages from appearing on iPad
Create an independent Apple ID for him; as a minor he will have to be added m to your family group with Family Sharing, which will allow him to access most of what you have paid for and ask for permission to buy apps / media.
Apple IDs were never meant to be shared.

Changing an Apple ID has some implications of course:


If you change it in the Game Center, progress associated to the old Apple ID will be lost on some games.
Apps bought or downloaded with the old Apple ID will keep asking for its password to update. If you download them again with the new ID most should work under Family Sharing (i.e., you don't have to pay again; it's a per app setting defined by the developer)