Can't really complain if they offer Spotify Family which gives you 6 separate premium accounts, I think it's only double the cost of a normal Spotify account.
So the solution is paying double so I can log out of my own account and into an account I created for my 2 year old so we can listen to a disney song? And when I want to listen to my own songs again then I have to log out of my kids account and back into my own?
Yes, if you want multiple accounts you pay for multiple accounts. It's a solved problem you just have to pay the $9 a month.
I have two children, myself. I just installed second account on an old phone which has no SIM card in it, it has all the kids playlists and I don't have to worry about them getting recommended any of my 90s thrash metal. :)
That unfortunately doesn't solve it. There will always be moments where kids will want to ask for songs on your Spotify, like you're renting a car and have your phone hooked up.