Because I'm starting to feel like an overprotective mother (and I so am not one of those!). All the other children in the street don't wear helmets, and my DDs are so good at keeping theirs on, but I know it annoys them.
The thing is that, unlike most of the decisions DH and I have made about parenting, we've just swallowed the standard advice about helments, without researching the ins and outs of them. So what's the deal?
Am I being overprotective? Or haven't I read enough research and arguments to make an informed decision?