The assumption of adults is the reason why. Adults perceive a cushioned and "padded" sole as particularly comfortable and want to get the feeling of walking like on clouds.
It actually prevents that one perceives the underground. For example, children can be tempted to jump from greater heights, so that injuries are more likely to be provoked, because a thicker sole prevents the direct sensory feedback emanating from the sole of the foot on the respective surface.
If the sole is too thick, the child cannot feel the ground properly. With our very thin sole this is possible again, because it also allows the foot to balance itself and thus to challenge and promote the foot muscles.
The sole of our barefoot shoes is 2.5mm thin. We have tried to create as little of a sole as possible but as much as necessary to protect the childs foot from wetness, cold and spiky stones.
No, that cannot happen. If the child can feel the ground, it gets direct sensory feedback and runs, jumps and climbs more carefully. It moves much more liberated and independently through its environment.
Yes, the sole offers sufficient protection on any surface.
Basically, you only need to protect your feet from sharp or spiky objects.
Fortunately not with children! With adults and "mature feet" it should be handled differently. Adults feet are usually not used to the "normal" strain, anymore.