How do you play family purchased music with Apple Watch?

We have a family sharing group that includes myself, my girlfriend, and her two kids. The kids have Apple Watches and we'd like to share music from our extensive library of purchased music (we do not have Apple Music) with the kids. I can see all of our purchased music on my Mac in the Purchased section of the iTunes Store.

How can the kids get to the purchased music from their Apple Watches?