My photos are appearing on another device and they are not shared
I've set up my old ipad with a new apple ID for my son. His account is not logged into the ipad and some of my photos appear in the photo app. They are totally random, not in a shared album.
If I delete a photo on the ipad it removes it from my phone. Any photos he has taken on the ipad do not appear on my phone.
How can I fix this??