First of all, if you think every mother in this country is adequately explaining menstruation to their daughters, then you are really out of touch with society.
Second, if you are worried about your children being exposed to age-appropriate health information about their bodies, then maybe you should look at home schooling them where you can fully restrict access to what they are being taught.
Third, show me a health science curriculum that teaches 11 year olds about sexual reassignment surgery, since this seems to be a boogeyman that's keeping you up at night. I really do want to see a curriculum that has this information in it and how it is presented to them.