Family sharing

Your child should have their own AppleID - in fact, every user should have their own AppleID. This is essential to maintain intended separation of activities and to avoid unintended sharing of sensitive and data.

You may find this information to be helpful with setting-up an AppleID for a minor - and considering appropriate controls:

Apple for Kids - Official Apple Support

Help your child set up an iPhone, iPad, or iPod touch - Apple Support

Family Sharing and Apple ID for your child – Apple Support

Use parental controls on your child's iPhone, iPad and iPod touch – Apple Support

If you have been sharing your AppleID with your child, so as to ensure proper separation between AppleID accounts, you would be best advised to completely erase and the iPad - and setup from scratch with the correct AppleID. This will remove any personal and sensitive information (such as your own keychain/passwords) from your child’s device:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Perhaps you didn’t get to the final paragraph…

… you would be best advised to completely erase and the iPad - and setup from scratch with the correct AppleID. This will remove any personal and sensitive information (such as your own keychain/passwords) from your child’s device:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

If you have already set-up the iPad with your own AppleID, your own personal and sensitive information (e.g., Saved Passwords, Calendar, Notes, Contacts, Messages, Reminders etc.) will likely have been synchronised with the iPad. In just signing out of your own AppleID - and signing-in with another - your sensitive data will be merged with that account that you subsequently sign into.

So as to prevent the data merge, you should properly prepare the iPad using the appropriate procedure. If you don’t use the correct procedure - and are willing to both accept and live with the consequences - you can follow the path of your own choice.

You may wish to start with this link:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

You are very welcome.