I allowed my child to install various apps on her iPhone
It sounds like you may have granted persmission through Ask To Buy in which case you can't in your situation, sorry.
From: "Prevent in-app purchases from the App Store" --> Prevent in-app purchases from the App Store - Apple Support
- "You can control purchases on an Apple device in a few ways:
- If children in your Family Sharing group have their own devices, use Ask to Buy ( Approve what kids buy with Ask to Buy - Apple Support ) to screen and approve their purchase requests. However, "If a child redownloads a purchase, downloads a shared purchase, installs an update, or uses a redemption code, the family organizer won’t receive a request. "
I don't know if ScreenTime may help you if in-app purchases are involved.
Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support
Others have had similar requests so you may wish to send feedback to Apple. Click on this link for Apple products feedback links --> Product Feedback - Apple
Apple may not respond but your comment will be read.