Family Sharing
How do you add iMessage to family sharing on a child’s account on an iPad Air 3 from the iPhone XR
iPad Air 3 Wi-Fi
Question marked as
I'm not sure I understand what you are wanting do, but Messages is for use with a single Apple ID. For a family to share Messages, you would need to pick an Apple ID, and each family member would need to log in using the same ID. If you are trying to monitor your child's use of Messages, you need to sign into Messages using their Apple ID.