Metal lawn edging strips

Correct. In kindergarten we had wood chips. There are also splinters but it is much more pleasant than bark mulch.

Never seen this with us, 90% sand or gravel, sometimes grass or rubber mats.

I also find the wood chips quite pleasant to walk on (although I have never walked barefoot on them), and I think they give way very well. In contrast, in my opinion, the rubber mats are almost dangerous. They may absorb the vertical forces quite well when falling down, but they cause beautiful abrasions or burns when falling.

Even though the wood chips are not exactly cheap and it will be a huge amount if I have to lay them 30-35 cm thick, it is probably the best choice.

I would also be interested in the transition. Does anyone have wood chips (or bark mulch) at a climbing frame? How do you handle the transition? Smoothly without separation, with a metal strip, with borders, with lawn edging stones, ....?
Feel free to include photos as well.

I also had some to click and they were fruitful in processing.

failed, sent away

Even though the wood chips are not exactly cheap

I'll link internally to another post here in the forum: https://www.hausbau-forum.de/threads/Haus-bilderthread-zeigt-her-eure-hausbilder.14011/post-405903 Haven't checked it, but maybe the tip helps...