Prevent iTunes & App Store purchases
Prevent iTunes & App Store purchases
You can also prevent your child from being able to install or delete apps, make in-app purchases, and more. To prevent iTunes & App Store purchases or downloads:
1. Go to Settings and tap Screen Time.
2. Tap Content & Privacy Restrictions. If asked, enter your passcode.
3. Tap iTunes & App Store Purchases.
4. Choose a setting and set to Don't Allow.
You can also change your password settings for additional purchases from the iTunes & App Store or Book Store. Follow steps 1-3, then choose Always Require or Don't Require.
Taken from Apple's Support Page