My kid - 2 LZ. Freak fall. Another kid - blades went out from underneath during stroking. Freak fall.
You can put as much padding on your head as you like, you're still going to end up with concussions. The helmet/padding will prevent a skull fracture - but, the concussion happens when your brain sloshes against the inside of your skull ... it's a shock wave impact. The brain gets bruised. Which is why each successive concussion is generally worse, particularly when someone hasn't taken adequate time to heal; think of getting a bruise on a bruise ... the blood vessels are already compromised and the second impact is on an already weakened structure.
There are studies going on about how to reduce the factor of concussion ... neck supports, mouthguards etc, but so far, nothing is proven ...
The BEST prevention is learning how to fall. Martial arts is excellent; you learn how to tuck, roll, react fast, protect the head ... that's saved us from quite a few nasty head injuries.