It does appear that some councils are far too willing to impress adult perceptions onto young minds which are clearly not capable of the correct level of intellectual understanding.
Once again, the pendulum has swung too far - from children being woefully under-educated in matters concerning reproduction and sexual health, to as you quity rightly say AOG - 'too much information'.
The golden rule regarding education to any age group about any subject is - information at the level of the recipients' comprehension.
For the same reason you would not start debating the ethics of Hitler's Final Solution with three-year-olds, you would not start using words like 'vagina' and 'sperm' to five-year-olds.
This wooly-headed over-liberal nonsense will saimply lead to confusion and fear for young minds, and is patently wrong.
Literacy, is, as you confirm AOG, woefully under-taught due to the constrctions of the National Curriculum (another good idea poorly thought through and implemented) - and this forcing of 'over-education' will simply take up valuable time from that essential plank of basic education.
I for one would withdraw my child from these classes, if I had a child of primary age.