I don't have kids, but I do have rent and bills to take care of, along with trying to save up a nest egg for the future when I do have kids.
My solution to wanting to change my career from teaching to illustration, while still needing money to survive, was to move from full-time to part-time work. I cut back as much as I could, which was actually pretty substantial since teaching pays well here, and we have socialised healthcare. I only teach two days per week now. I earn just enough to cover essentials.
Obviously, I'm in a privileged position. (Getting that teaching degree was a good move.) But when taking a look at your own situation, how much money could you afford to lose each week? What expenses could you cut back on to make that work? Do the math and determine how many hours you can afford to lose.
Even one extra day per week which you don't have to work will make a world of difference as a creator trying to put something out into the world.
Your idea of just creating a very loose, rough work is a good one, too. That way you can practice pacing, storyboarding, and get your story out of your head and into the world in a time-efficient manner. Plus, once it's done, that 'first draft' may be something suitable to pitch at publishers, if you couple it with some refined examples of what your full-effort art actually looks like!
