i don't want my child to have access to previously downloaded apps

See the following from Hide purchases from the App Store - Apple Support

When you hide an app, it won't appear in your list of purchases in the App Store. If you use Family Sharing, the app also won't appear in family members' purchases and won't be available for family members to redownload. But the app will still appear in your purchase history.

Hiding an app won't remove it from your device, a family member's device, or other devices that are signed in with your Apple ID. If you want to remove an app from the Home Screen, customize the Home Screen on your iPhone.