Outdoor area, slope towards the neighbor, how to frame?

We have already caught the slope with curbstones, see picture. Now it's about going over the crest at the top. How should we do that best, just grass? A wall? Fence? Of course, it's also annoying if Junior's ball keeps rolling down again. What would you do?

Hello again,
I took 3 more pictures from the balcony,
what would you do with the edges, toward the playground? At the corner, a garden house should stand someday. To the left of it, a barbecue area, then my bed.
Regarding the neighbor in the wooden house, we are still clueless as always, maybe a wall after all?
Hard

How about a raised bed then? Like for the edge. It doesn't have to be particularly high, just so you have a boundary there and maybe also some wind protection.

How about a raised bed? Like for the edge. It doesn’t have to be particularly high, just so you have a boundary there and maybe also some wind protection.

Actually a good idea. There are supposed to be 2-3 trees there as well, raised beds in between, I'll think that over.

I see it the same way as : Ground covers are wonderful. You could also grow berry bushes, but it takes a while until the gaps are closed. If the soil is right, azaleas and rhododendrons are also a very nice alternative - you just need some patience until it is "closed." Fence or not – we would need one because of the hunting dog, but for our children, we would not have needed one.

Is the playground public or is that your garden? Why a wall?