There was that thread recently about the boy who wanted a dress and some interesting discussions around how perhaps our difficulty with cross-dressing is that we value women less in society.
On the other side of the coin, I went to the Science Museum today with my DC. I suddenly realised that in the Garden which is the area for 3-6 year olds and my DC were playing with a water installation thing, that there were no girls playing with it at all - there were about 15 children, all boys (I don't have any DDs). So I carried on looking at the numbers of girls vs boys as we went round the rest of the museum out of interest and girls were noticeably outnumbered, I would say as much as four or five to one. Obviously once children get older they have a greater say in what sort of activities they do with their children but under 6s are pretty much at the mercy of their parents.
I think it's really sad that it obviously doesn't occur to many people who only have DDs (the only girls I saw were with their brothers) that science is something they could/should be interested in. Surely starting young is critical to getting them interested in something?