Can two iPhones be synced together?

I'm going to give you 3 links, which I recommend you read.

1. What to do before you give your phone to someone --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
2. How to set up a phone for a child --> Set up a device for a child with Family Sharing on iPhone - Apple Support Your son needs to have his own unique Apple Account. It should NOT be your Apple Account.
3. Use Parental Controls on your sons iPhone --> Use parental controls on your child's iPhone or iPad - Apple Support

Sorry, what you ask is not possible.

Maybe if you could explain what it is that you are trying to accomplish, we might be able to help.

By sync what do you mean? What are you trying to accomplish?