From a 35 yo, with a child, background dirt poor parents who has basically been struggling my entire life (to give you a point of view of my comment). Go for the higher paying job.
Something that is secure, and has a smaller chance of everything collapsing on you, is a main requisite. I have similar issues (family to support, more bills than income).
You don't want to be in this position. It's more difficult to claw your way from the bottom than it is to keep afloat.
Unless you are certain that you can find your idea and keep afloat enough to cover everything, I wouldn't risk your current position.
But take this with a bag of salt, but remember my warning - if there is no safety net, you are not the only one to suffer.
Edit.
Is it somethig. You are able to start in your free time (you're lucky to have any, so use it wisely!) If so I'd say keep working on it u til you get some sort of traction.
Second edit : it's what I'm doing. 70+ hours a week to support my family, and what time I can scrape together to work on my side project.