I don't know for sure, and if I am wrong I am sure somebody will be able to correct me, but I strongly suspect most, not all, but most teenage pregnancies are the product of chavs having sex.
14 and 15 year old chavs will, I suspect in many instances, also be the product of teenage pregnancies, so it is simply a case of monkey see monkey do.
Sex education will never stop this happening.
Whatever, any level of formal sex education for a 5 year old is wrong. This is not head burying and I don't advocate The Stork - A cosy little chat with mummy or daddy saying babies come from a mummies tummy is one thing, but for a 5 year old a formal curriculum lead sex lesson is wrong.
10 year olds - fine, 5 year olds, definitely not.