why I cant install new apps on my child iphone

Hey DJ7670,

It sounds like you're having an issue with Ask to Buy. We'd recommend reviewing the information in this article as it provides steps to help resolve that: If Ask to Buy isn't working - Apple Support

"Review your Family Sharing settings

If you're the family organizer, you can go to your Settings or System Preferences to see if your family members' accounts have Ask to Buy turned on. 

On your iPhone, iPad, or iPod touch

1. Go to Settings.
2. Tap Family. If you don't see Family, tap your name, then tap Family Sharing.
3. If you're the family organizer, make sure that Purchase Sharing is turned on. Then you can tap a family member's name to see if Ask to Buy is turned on for their account.

On your Mac

In macOS Ventura or later:

1. Choose Apple menu  > System Settings.
2. Click Family.
3. If you're the family organizer, click Purchase Sharing and make sure that Share My Purchases is turned on.
4. Click a family member's name, then click Ask to Buy to see if it's turned on for that person. 

In macOS Monterey or earlier:

1. Choose Apple menu  > System Preferences. 
2. Click Family Sharing. 
3. If you're the family organizer, click Purchase Sharing and make sure that Share My Purchases is turned on. 
4. Click Family Sharing and click Details next to a family member's name to see if Ask to Buy is turned on for that person."

Thanks!

Hey DJ7670,

Please don't hesitate to let us know if you need additional assistance.

Take care.