Your description might suggest that you are sharing (or have previously shared) your AppleID between devices. Sharing an AppleID seriously risks information leakage between users and devices. Each user must have their own unique AppleID; remember the iOS/iPadOS system architecture assumes that an iPad or iPhone is a single-user device.
If you have previously shared an AppleID between devices - even if you don’t now do so - it is possible that your Keychain Data (i.e., your Passwords) have been merged with your child’s AppleID account. For now, I’ll refrain from explaining the mechanism by which data is unintentionally merged between AppleID’s.
If unintentional data-merge is the cause, then you’ll need to delete each credential manually from your child’s account.
Should you ever change the primary user of an iPad, if you wish to avoid accidental sharing of data between devices and AplleID accounts, you must follow this process:
https://support.apple.com/en-gb/HT201351