How to set parental control

You have several options:

• You can prevent all purchases by removing the App Store by going to Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Installing Apps, and turn this switch off. This will not allow a person to use the App Store at all.
• You can use the Ask to Buy option when the child is part of a Family Plan.

Approve what kids buy with Ask to Buy - Apple Support

• You can require the Apple ID Password for all purchases

Require a password for App Store and iTunes purchases - Apple Support

• You can prevent a child from making in-App purchases

Use Screen Time to prevent purchasing - Apple Support

This support article also has other features you can enable using Parental Controls

Use parental controls on your child's iPhone and iPad - Apple Support

This may help:

Use parental controls on your child's iPhone and iPad - Apple Support