Do you have the problem all over the ancient place or are these stuck spots located near where the ancient place and the flowers/bushes meets (the bottom of the ancient place)? If it is only the spots I have a solution for you:
When you see a pebble in those stuck spots, drop the kid a bit above the pebble, that is closer to the middle of the ancient place, and not right on top of the pebble. The kid will pick the pebble anyway, because the pebble area is wider than the pebble itself. I'm sorry for not finding the right words here, but I hope you understand. The pebble area is the sensitive area surrounding the pebble that makes it possible for the kid to see it and pick it up.