[kempbellt]

The most likely outcome from all the scenarios you mentioned is that nothing happens. Kids do these things all the time and are just fine.

Injuries occur occasionally, and even less frequently are those injuries fatal.

A friend of mine supermaned head-first into a tree while snowboarding last year. The tree was probably a foot in diameter, and he was going fast enough to shake snow off the whole tree. What happened? Nothing. We all laughed about it and kept snowboarding.

We are pretty resilient creatures when it comes to impact damage.

Drowning though, completely different. Much like filling a car's oil intake with dirt and then having the engine immediately seize. If you start breathing in water, you're do some serious damage to your lungs and cutting off oxygen to your brain, and further inhibiting basic survival functionality, and quickly resulting in death, if not remedied immediately.