I have recently seen some trample guides explain that the stomach should not be stepped on. I wonder why that is if there are people out there that love it... I actually would love to try feeling the weight of a girl or 2 on my stomach.
And for those people that like being trampled? Do you completely relax your stomach when a girl is standing on it?
Injuries can occur doing anything. It is rear unless an adult tramples a toddler. I do prolong tramples and sittings. If you have sunken right down to the spine then after 45 minutes toxins can build up. The toxins are caused by blood flow restrictions.
Punching can leave bruising but seldom can cause life threatening or permanent injuries. Rolling car over the belly is different from being hit by the car. Compressing the stomach against the heart can stall the heart so if you are becoming weak release the pressure.
Otherwise it is safe as sitting on your rump.