Install apps on child’s Apple Watch using Family Setup

my 10-yr-old son has a new Apple Watch SE 2 set up through my iPhone. No matter what app he chooses on the App Store on the watch, it won’t install. It takes his AppleID password, then asks him to dbl-click the button on the watch. But then it just heads back to the App Store screen with the “get” button ready to be pushed again. It never downloads or installs the app. It doesn’t seem to matter if he’s on WiFi or cellular data. Anyone else run into this and have any ideas?