Music On Apple Watch

We purchased an Apple Watch SE for our son as a stand alone watch. We used Family setup to set it up because it is not tied to a phone. He has a number and an iCloud account. He has a music library on his iPad with that iCloud account. I cannot figure out how to get music on his watch so he can listen to it on the go. When I open the Watch App on my phone there is no music in the list of apps. On his watch itself it says that any music added to his library will show up here, but that is not happening. Has anyone figured this out?