What if they just ask your age as step 1 of the setup?

I know JBL has wifi enabled bt speakers that would be an all in one. You’d still need your phone to initiate it. But being wifi it should be fine to walk away after starting the stream.

Any assistant (assuming they’re still available) would be able to play music at night (a used Google mini) or similar.

We were building our house when my wife was pregnant, I put ceiling speakers in all the bedrooms so that is what we used. I built a diy whole house audio system which we did use to play sounds/music at night in my kids room.