Screen Time: contact management request never appears
I am trying to set up Screen Time for my 4-year old son's account. Specifically, I want to enable managing his iCloud contacts remotely. When I turn this option on, a new row appears with the greyed-out text "Contacts Pending" and below that "Contact management request sent to *****. You can manage *****'s contacts after the request has been accepted." But I never see any request on my son's device.
I have an iPhone XS running iOS 13.4.1 and my son is using an iPad Mini with Retina Display running 12.4.6 (iOS 13 is not supported on this device). All other Screen Time features seem to be working apart from this. I've searched the web but can't find any references to this specific problem.
iPhone XS, iOS 13