I wish to transfer an old device to my son with a diferent SIM card and phone number

Getting him a new, different ID would be best. Apple IDs aren't meant to be shared.

Follow the steps in the article below to make it 'his' device.

Selling/Giving Away Device.  

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.        

Set up - your child’s iPhone, iPad, or iPod touch