Two families challenged the schools in Lexington, not over the decision to make the books part of the curriculum, but for not allowing the parents to have notice of what is being taught, and an opportunity to "opt out".
A Federal District Court favored the schools. Although the District Court acknowldeged that parent have a constitutuional right to direct the education of their children, parents don't have a right to say "how" their children will be educated. The Court found that the school is not compelling these very young kids to believe anything, or to hold beliefs contrary to their parent's upbringing and guidance. Nor are the parents prohibited from teaching a contrary message at home. Part of the Court's reasoning here is that Massachusetts permits gay marriage. In the end, the parents get no say in what their kids are taught, and cannot refuse to have their kids participate in lessons that are fundamentally at odds with the parents desire for their kids.
I might agree with the Court if the kids at issue were older - capable of discerning the source of the conflicting messages, and capable of deciding which of them they choose to believe or respect. But, 5 and 6 year old kids don't have this discernment as a general rule. If you live in Massachusetts, your kids better grow up quick...there's no time for them to learn about primary colors, animals, shapes or letters. They need to be getting into politically correct thinking before the schools deal with education.