It's ironic that the weight of the helmet is what actually causes the risk of injury. Without it, there's any number of safe ways to carry a young child.
If I wanted to carry a very young one, I would put them in something like a BabyBjorn carrier. You'd need an upright bike, but it should work.
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Maybe the Americans and English have thin skulls or something. The Dutch have miraculously survived their non-use of helmets without killing off their population. Maybe it's the extra exercise that's toughened them up
...yes, I realize their roads are more bike friendly, but I'm not talking about carrying your kid out on an arterial road... 99% of family rides never leave the quiet suburban neighborhood, or the bike path with no cars at all. Those are the rides that people are scared to take.
I feel bad for my daughter who will be forced into a helmet by nanny laws.