"Teachers that attempt to teach minors about homosexuality should be charged with child abuse. Why isn't that law on the books already?"
Because many of us traditional Americans have been asleep at the wheel on this one. Their ideology is that homosexuality is a naturally occurring phenomenon and therefore only religious bigots say it's wrong.
The political leaders within the gay movement have made their aims and goals very clear in their publications since the 70s. And teaching children about homosexuality is one of their many efforts to have homosexuality and gay marriage completely legalized and "normalized". The next steps will be
1) to silence any criticism of the practice; this is already the law in Canada, where pastors of Christian churches can be jailed for reading the Bible prohibitions against homosexuality,
2) to lower the age of consent from 17 to 12, or even younger. This means your middle-schooler could be in a relationship with his soccer coach and there would be nothing parents could do about it if it were a public school.
Parents are beginning to fight back. But they've been slow on the uptake, since these goals have been published for 30+ years.