Hi Rjmc779,
Approve what kids buy with Ask to Buy outlines the feature whereby requests for apps or purchases are sent to you. In that article is the following section:
"Where to find your Ask to Buy requests
If you miss an Ask to Buy notification, you can find the request in Messages on your iPhone, iPad, iPod touch, Apple Watch, or Mac. If you don't see the request in Messages, you can find your Ask to Buy request in Notification Center. "
Confirming that the notifications for your iPhone are set up properly and checking the Notification Center of that device next time a request comes through are good steps to follow.
Regards.