I have been googling and pinterest searching this but can't seem to find any good ideas - hoping one of you has a similar situation!

Our backyard is two levels, it's basically sunken in, so you walk down stone steps to get to the lower yard, and next to it is a stone retaining wall that borders the upper yard. It's about a 5 foot drop from the top to the bottom, and its all open right now. The upper yard is sloped, so it meets the lower yard at the bottom, and there is an opening at the bottom.

SO when kids are playing, they can easily either go up the slope to be on the upper level, or go up the stairs to be on the level - and then they could super easily jump or fall off the edge. Basically backyard play requires LOTS of supervision and we'd like a temporary fix to make it safer.

Any ideas for something temporary / cheap to make this safe until they're old enough to know better?

I attached a pic but this isn't our yard, I'll take a pic soon!