Shouldn't the Freedom From Religion Foundation sue the Madison school district for the extensive celebration of a religious holiday?

From the Madison Metropolitan School District website:

Kwanzaa celebrated at two schools

Students and staff at Falk and Lowell Elementary Schools recently performed and displayed art projects that reflect the principles of Kwanzaa. The culmination of a semester’s work incorporating Culturally Relevant Practices, the celebration also featured the donations from the schools' service learning project to help build a school library in Ghana. Four MMSD elementary schools (also Hawthorne and Mendota) are working together to provide Culturally Relevant Practices and experiences for all their students.

Video of Madison teachers and children celebrating Kwanzaa at the link.

The school district will surely say that Kwanzaa is not a religious holiday, but what constitutes religion for Establishment Clause purposes? It's not an easy question. I say that as someone who has taught a law school class in Religion and the Constitution for many years.

I once gave an exam that challenged students to think about Establishment Clause problems inherent in an invented state program pushing environmentalism, defined by statute to mean "the belief in the importance of honoring and conserving the Earth’s resources, minimizing the impact of individual human beings on the Earth, and understanding one’s personal duty to inspire others to honor and conserve resources and to minimize human impact on Earth." In my hypothetical, schools were required to stage day-long Earth Day celebrations every year, praising nature and inspiring conservation, and teachers had to begin each school day with a "solemnification exercise" that included "a recitation enforcing the values of environmentalism along with a set of symbolic gestures," with this example, described in the state law:

On a small table, the teacher unfolds a green cloth to reveal a twig, a small stone, an egg, and a small box of good soil. The teacher opens the box, takes out a bit of soil and sprinkles it on the stone, egg, and twig, and says: "This is our Earth, which is given to us, to love and preserve, for all time." The students then repeat that phrase aloud, and the teacher carefully closes the box, rewraps the items, and puts them away.

My hypothetical environmentalism, like Kwanzaa, is at least a religion substitute, in that it attempts to capture the children's idealism and spiritual longings and to direct them into a particular ideology. It employs the devices of traditional religion: songs of celebration, symbolic gestures and rituals, incantations. In the case of Kwanzaa, based on what I've read, it was originally designed as an alternative to Christmas. And the 7th of the 7 principles of Kwanzaa is:

Imani (Faith): To believe with all our hearts in God, our people, our parents, our teachers, our leaders, and the righteousness and victory of our struggle.

Presumably the God part is watered down for school purposes, but watering down religion is a problem in itself.

ADDED: I see that at something called "The Official Kwanzaa Web Site" — what makes it "official"? — the "Imani/Faith" principle has no "God." It is otherwise word-for-word the same as what I've quoted above. Without God, the statement of faith is puzzling: believe with all your heart in our people and the righteousness of our struggle. That sounds like the worst of what governments have done grabbing at the hearts of young people.