Family sharing

If you set up Family Sharing, each person can have their own Apple ID.

If 13 years old or older.

Apple ID - create a new.      

Apple ID – Create         

If under 13 years old, you will need to set up Family Sharing to create an ID.

Family Sharing and Apple ID for your child.      

Family Sharing.         

Family Sharing - Set up.        

When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. Also set up Family Sharing between the IDs to keep access to your apps/purchases. 

How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.        

What to do after you change your Apple ID or password - Apple Support.     

No. The entire point of Family Sharing is that every member uses their own Apple ID.

If everybody uses the same Apple ID, then Family Sharing is entirely defeated, since an Apple ID already has access to all its own Purchases and Subscriptions. Theres no Family Sharing when the same Apple ID is being used.

Create an Apple ID for your son, and invite it to Family Sharing. That way each person gets their own independent Music And video Library.