Yep, now look at my parents, they never wore seatbelts as children, and they survived OK. So obviously, all that stuff about seatbelts saving lives is rubbish.
Sorry, this is a sore point for me. Martianbishop has explained far better than I can, why proper controlled studies give you a less biased picture than everyone sitting around sharing stories (not that I'm knocking the latter, it's a great thing to do).
Mumsnet is useless as a representative sample of the population.
If you're on mumsnet that means you have access to a computer, which suggests in turn that although you might be struggling to pay the bills, you're probably not living in a cardboard box under a bridge. You're also reasonably well educated, because (by definition) you can read and write.
Now, it's a well-known fact that health is strongly related to socio-economic thingies like income and education.
Mumsnetters and their children are almost certainly more healthy than a random sample of the population. So when 5 or 6 (or even 10 or 20) mumsnetters are saying "well, my children are healthy" it proves zip-all about anything - it's just what you would expect.
Please, let's not bury our heads in the sand about possible risks to our children, however hard it may be to accept them.