This is how every single music recommendation system works, though. If you listen to metal, you get metal recommendations. If you listen to immature poop songs, you get those back too.

There isn't a switch you can flick that adds taste to your kid's listening habits. There isn't a single paid music service that offers that, outside the parental controls switch to disable explicit music. Spotify won't change this because their highly-relevent feedback loop is why people (myself included) still pay for their service in the first place.

I wish you luck, but being angry at Spotify for not changing your kid's listening habits is a bit solipsistic.