No I dont but I imagine what you are saying is correct. I would be worried all the time. I would grant them - by todays standards - extreme freedom though, as I value freedom over safety. But sure, it wouldnt be easy on my head and heart!
In a lot of countries we dont have chalk cliffs that just randomly collapse. If I go and look over the edge at a cliff in Gothenburg, theres close to zero danger as long as I dont **** up and fall over. Sure theres a minimal chance that would happen but theres a minimal chance a piece of space...
How is she endagering them any more than if they were walking next to a road? They are kids, not lemmings, they are very unliklely going to jump off the cliff randomly.