How can I stop family contacts from syncing to my child's iCloud?

My and my husband's contacts are suddenly appearing on our child's device. I have checked all of our iCloud accounts: my husband and I haven't added my child's account to our contacts and our child's device has contacts registered under their iCloud only.

We have family sharing, but our contacts weren't syncing there until recently. I can't figure out what is causing it, help please. This needs to be rectified and I am seeing others with similar issues. This shouldn't be so hard to figure out.

The only icloud account on our child's device is their own. I do not want them to have our contacts. How do we rectify this?

[Re-Titled by Moderator]