Family Watch not showing apps installed on iPhone

I used my iPhone (Xr) to set up my son's Apple Watch (Series 5) as a Family Watch. We would like to load some apps, such as Spotify, on the watch which are already loaded on my phone. When I select his watch from the All Watches menu and scroll down, it does not show any third party apps. It shows only the Apple installed apps on my phone (Find My, Messages, Photos, etc.) I've deleted and reinstalled the watch, restarted the phone, restarted the watch. Nothing seems to address this problem. Any help much appreciated!