I had to come back to this thread to add more points.
Richmal Crompton was a classics teacher - she would be well aware of innuendo and outright references to sex in ancient literature. Lysistrata by Aristophanes being the most obvious one. I don't believe she was innocent at all in deciding on a giant cock for the maiden aunt.
I think some of the innuendo in the childrens' books was deliberately put there to amuse the adults who had to read them to the children. It's much same today in that modern childrens' films have jokes for the adults so that they will take their kids to the cinema or buy the dvd.
Smutty innuendo has been around for generations - but the beauty of innuendo is that you have to understand it to be offended. So those who are outraged can't admit to it.
