Hey there ddunstan,
It may help if you turn off Screen Time completely, restart your son’s devices, then turn it back on. Go to Settings > Screen Time and scroll to the bottom and tap Turn Off Screen Time. To restart, follow the steps below for your son’s device:
How to restart your iPhone X, 11, 12, 13, or later
1. Press and hold either volume button and the side button until the power-off slider appears.

1. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
2. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
How to restart your iPhone 6, 7, 8, or SE (2nd or 3rd generation)
1. Press and hold the side button until the power-off slider appears.

1. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
2. To turn your device back on, press and hold the side button until you see the Apple logo.
How to restart your iPhone SE (1st generation), 5, or earlier
1. Press and hold the top button until the power-off slider appears.

1. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
2. To turn your device back on, press and hold the top button until you see the Apple logo.
You can read more here:
Use parental controls on your child's iPhone, iPad, and iPod touch
Restart your iPhone
Take care.