Seriously?

During this coming week, there is legislation in the UK set to be voted on in the British House of Commons, deciding on whether to start Sex Education in Primary School.
This is in fact to ridiculous to think about, but I am simply unsure what any reason in favor of this could be... seriously - why would it strike you as something reasonable to do in primary school? Kids don't know yet what a square root is, and how to construct complex sentences, but that is already on the timetable? It just strikes me as very, very odd...