A Kid's First Book About Sex by Joani Blank & Marcia Quakenbush

For parents and or guardians to use to teach young children about sexual activities, nudity, alternate gender/sexual ideologies, masturbation and orgasms.

This book contains: alternate gender/sexual ideologies, discrimination commentary, grooming, sexual discussions, sexual activities, and sexual and non-sexual nudity.

This book was written back in the 80's, it was intended to be used for parents and or guardians to read with their children not as a school library book.  

Why is it in a school libraries for kids, not parents/guardians to check out and is it in the teacher's classrooms where the books are not cataloged?