The theory behind helmets or lack thereof

Allegedly the theory behind the helmet law (which went into effect 15 December, 2007) is that children's skulls are so soft that it does more harm than good to have a helmet. Plus, there aren't any helmet manufacturers out there to date that make them small enough. It doesn't sound that different from our no-seatbelts-in-buses theory; that somehow it's safer to NOT be buckled in to a tipping/spinning bus with 6 foot ceilings.