The problem is it is not quite so simple as you make it out. Kids are often told when a mommy and a daddy really love each other their love creates a baby. What happens if Johnny, a 5 year old, asks what happens if there is a daddy and a daddy. How far should the teacher go? No matter how the teacher answers it is going to cause issues.
Why not let the parents who know the child better explain these things?
In terms of a parent's profession there is nothing age inappropriate about an architect. There is certain age inappropriate things about sex. A teacher does not know if a kid has hit puberty, how mature they are, etc. This is why a parent should be involved with this not teachers.
How many 5 year olds are paying attention to laws being passed? None. The only reason they would know is if their parents or teachers tell them. I think kids should be kids. You shouldn't be telling kids about cultural / legal things that are going on if you can avoid it. I have no idea why so many people want kids to get involved with legal discussions. Just let kids be unaware of the strife, conflict and other things that don't matter to them in the world.
I don't want to talk to 5 year olds about taxes. Does that mean I want conversations about taxes to be taboo? I just think there is a time and place for things like this and teaching 5 year olds about this stuff is too early.
Also, I would note that the law only bans classroom instruction. If a student asks a teacher outside of that context the teacher could answer.