Earning money without earning it directly from YouTube ? Patreon.
Changing niche on a channel with 200K+ subs is high risk.
Presumably those people have all subbed because they like kids nursery rhymes.
So if it's a big departure expect mass subscriber departures.
What niche did you have in mind? Given you'll almost certainly have told youtube that you content is for directed at kids; you wouldn't want to start uploading videos not suitable for kids on that channel.
Almost certainly the best option of wanting to do something very different is to start a new channel for that content.
When you say "demonetized" do you mean that it has never been monetized, or that it was and YT has now
demonetized it? If the latter, what was their reason for doing so?