almost identical for me, we all cycle and the only time a helmet is worn is by the youngest when entering school, it's the rules(mine are 9, 12 and 14, shortly to become 10, 12 and 15), otherwise he couldn't cycle to school.
If any of us ever take up MTBing then I think we'd wear helmets.
You do get looks from other parents, my particular favourites are the ones casting disparaging glances having just driven their, often tubby, kids to school. If you spoke to them they'd probably come out with some guff, without a trace of irony, about how dangerous the roads near the school are. Then carry on as normal, parking where they like/can get away with and using mobiles when doing the school run.
I do wonder at people that get hysterical over the choice of others not to wear a helmet. There're so many more pressing global matters they could take an interest in that could have a much more beneficial impact.
Agreed, mine are 6, 10 and 12. They have helmets bought by their grand parents but I leave it up to them as to whether they want to wear it or not. I don't wear one and I will not preach to them that they have to.
I think that at times in the current society that we wrap kids up too much in cotton wool rather than allowing kids to be kids.