how do i restrict access to my passwords and accounts on my childs ipad

Easy. Do not share your AppleID between users. Every user should use their own unique AppleID.

Sharing an AppleID risks significant information leakage between devices and will introduce major unexpected issues - in particular with Apple Messages and Keychain.

Your best route forward is to prepare the the iPad to be used by your child by following this procedure:

https://support.apple.com/en-gb/HT201351

Next, ensure that an AppleID is created for your child. If your child is a minor, you should create an AppleID from within family sharing. If you child is older, then create an AppleID account using the standard process - and add this AppleID to the family group. Family Sharing will permit selective sharing of Apps, storage, media and family Calendars etc.

More info about family sharing and its setup can be found here:

https://support.apple.com/en-gb/HT201088

https://support.apple.com/en-au/HT201085

Using your child’s AppleID, set-up the freshly prepared iPad. If you have created a new AppleID, your own personal data (including keychain) will not be visible to your child.

I hope this information and guidance proves to be helpful in resolving any issues that you might have.