Bungee cord the kid to a fixed point if he keeps getting out of your grasp. Or lock the doors. Even the materials to fix that are going to be a couple of thousand. Not hundred. Thousand.

In this economy, the only people not working are the ones afraid to get dirty. Plumbers, electricians, framers, tilers, drywallers, HVAC companies, welders, machinists, and everyone else are screaming for good help. You'll start off well above minimum wage, and be taught a career that will feed your family. Make it happen.

Cheapest option would be to mitigate the danger like kudzu mentioned - fill in as much as you can with woodchips/mulch/dirt. Then if kiddo runs off the edge he'll be fine and quickly learn to not do it again because getting a face full of dirt isn't pleasant. And/or get a couple sections of cheap porch railing or something.

How absurd that I have a similar area in my yard...not as dangerous but no idea what these cracked ,uneven, pieces of concrete were for except to make a giant puddle after the rain. I started digging them up and found that everything under the sun was buried under almost the entire yard. Every project is an adventure. No drainage, rusty nails, toys, sinkhole which was a turn of the century cesspool which was huge. Our soil is clay and nothing drains. We have a super sump pump but basement is always wet. We are the lowest property on the block. All my grass died from lack of drainage and too much rain. Now I have a mawn instead of a lawn with 3 dogs. I am almost suicidal! The only thing that works is my garden from years of dirt and mulch being added. Time for help!!

It is actually worse now and guess what? It is raining again!!

Sounds like you're going to have to tackle it one step at a time. First you'll need a plan to figure out what steps are first!