If giving away your older model iPads, you would be best advised to properly prepare them - which will entail a full reset/erase - as otherwise your private and sensitive data (including your account passwords saved in your keychain) will remain accessible:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
Outside of Educational and Business environments, iPad and iPhone are principally single-user devices. Each user should have their own AppleID - this being used exclusively with their own devices. This is essential to maintain intended separation of activities and to avoid unintended sharing of unintended information and data.
You may find this information to be helpful with setting-up AppleIDs for minors - and in considering appropriate controls while continuing to share Apps and paid Apple services if you should choose to do so:
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 don't wish to properly prepare the devices for reuse and you accept the implications of sharing highly sensitive account information - if you still wish to preserve existing data with different AppleID, ensure that you have disabled the Activation Lock on each device that will otherwise cause difficulties in the future. You can disable the Activation Lock by disabling the Find My service from iPad/iPhone settings before trying to use a different AppleID account:
Settings > [Your Name / AppleID] > Find My > Find My iPad - set to OFF
Having disabled the Activation lock, you can now sign-out from your old AppleID:
Settings > [Your Name / AppleID] > Sign Out
While not recommended, if you intend to keep iCloud data that is locally stored on your iPad, accept the opportunity to keep a local copy of your data (e.g., Calendar, Contacts, Notes, Keychain Passwords etc.) - as otherwise this data will be wiped from your iPad as you sign-out from iCloud. If you decline to save a local copy of data, iCloud data will be automatically erased.
Also ensure that you have signed-out from Messages and FaceTime:
- Settings > Messages > Send and Receive > [AppleID] - scroll to the bottom where you will find your signed-in AppleID highlighted in blue text; tap and select Sign Out
- Settings > FaceTime > [AppleID] - again, scroll down the page to find your signed-in AppleID highlighted in blue text; tap and select Sign Out
After signing out, a restart of the device is recommended:
Restart your iPad - Apple Support
After restarting, you can sign-in to your new AppleID account from iPad settings - and also sign-in to Messages and FaceTime if necessary. Any iCloud data that you saved to your device during the previous sign-out will be merged with your new AppleID account. Other than manual deletion of data, this merge is irreversible.