Can my son use Apple Music on his Apple watch? It’s a shared family plan?

Hello jmince0930, 

Depending on his Apple Watch, he may not be able to search for music by typing, and would need to search for music using dictation or scribble. Check out how to use Apple Music on a managed Apple Watch in the article below:

Play music on a managed Apple Watch - Apple Support

"If you’re part of a Family Sharing group that has an Apple Music family subscription, you can listen to Apple Music on your managed Apple Watch as long as you have a Wi-Fi or cellular connection.

1. Open the Music app  on your managed Apple Watch, then do any of the following.

• Tap Listen Now to see music chosen for you based on your listening habits.
• Tap Radio to listen to Apple Music Radio and genre stations.
• Tap Library to browse music saved on Apple Watch.
• Tap Search, then type (Apple Watch Series 7 and Apple Watch Series 8 only), dictate, or scribble an artist, album, or playlist.
  • Note: Scribble is not available in all languages.
  • Tap a playlist created for kids and teens by Apple Music editors.
  • Tap albums or playlists you’ve added to Apple Watch.

2.Use the music controls in the Music app and Now Playing app to play and choose music."

If that is not working as expected, then reach out to Apple Support directly to help investigate the behavior. You can use the following link to reach out: Contact Apple Support

Kind regards.