To show my kids a bit about programming we made a simple rabbits-and-foxes simulation. Little dots moving around a rectangle drawn on the screen. The red ones were rabbits, would move mostly randomly, and would periodically make a baby rabbit. The blue ones were foxes and would chase nearby rabbits. When they caught one they'd eat it and make a baby fox.

Fun to watch but we found no matter how we set the initial counts of rabbits and foxes, inevitably there'd be a population spike of rabbits, which would cause a lot of foxes to be born, which would eat enough rabbits (sometimes ALL of them) that the rest of the foxes would starve and go extinct.

We tweaked all kinds of parameters about how they move and how they reproduce and nothing kept the system from oscillating into a broken state.

Eventually we added a "rabbit preserve" - an area rabbits could pass freely through but foxes couldn't enter. Just like that - the system was stable(ish). There would still be population peaks and valleys but as long as the preserve was reasonably large the rabbit population might crater but wouldn't crash.

Its a nice little project, easy to code and fun to watch