How to explain to a five years old who doesn't want to wear a helmet?
The bike doesn't move unless the helmet is on your head. It isn't a negotiation. Mom and dad don't want junior to break like an egg. That's why we wear seat belts, helmets. You wear yours too.
Use a cantaloup as an example of what can happen.
Humpty Dumpty. A Tale Of 2 Eggs. Both Eggs Sat OnA Wall. Both Eggs HadA Great Fall. One ofT h e m Cracked.Wearing HelmetSaved TheO t h e rOne!
You don't explain anything to a five year old. You just say, "No helmet? No bike."