How do I install Spotify onto my child’s Apple Watch which is connected to my iPhone through the family app?

How do I install Spotify on my child’s Apple Watch which is connected to my iPhone through family sharing. He does not have his own phone and the idea behind getting him an Apple Watch which can be connected through family sharing on my phone was to avoid getting him his own phone yet. When we go to Spotify in the watch App Store it say it requires a phone. Not being able to access apps like Spotify on his watch is not ideal