If we're going to quote statistics people can we at least get them accurate?
Road Traffic Accidents account for 50% of all traumatic brain injuries. This includes cars, trucks, motorcycles, bicycles, and pedestrians hit by vehicles.
So no, CARS do not account for 50% of brain injuries FFS.
Do you know how brain injuries occur in most car accidents? It's not necessarily that your head comes into contact with anything, it's the speed at which your brain hits the front of your skull when your seatbelt grabs you, because your head stops moving with your body but your brain doesn't. So wearing a helmet while driving a car will do sweet FA in these circumstances.
Yes the LIKELIHOOD of you being in a bicycle crash is low, but the CONSEQUENCES if it were to happen will be greater than for example walking because you are a) going faster and b) more likely to hit your head on the ground because you won't have time to put your arms out to stop the fall (due to going faster).
But do carry on allowing your children to go out without helmets after all, it'll NEVER happen to them, right?