According to Advocate.com:
The plaintiffs cited a musical segment of Family Day that included nine separate performances by Christian groups, while children's entertainment at the Keiki Stage in Kapiolani Park had a stated purpose to "save souls." In its suit the ACLU claims the city did not allow equal access for all organizations to perform in Family Day events and instead invited select groups to provide entertainment. ACLU legal director Brent White said the city's actions are part of a "broader policy and practice of using city events...to provide certain religious groups special access to large audiences [so] they can spread their message. This mixing of government with religion is forbidden by the Constitution."
Even a Christian minister, Reverend Vaughn Beckham, has joined the plaintiffs, arguing that the city has participated in a scheme to promote fundamentalist Christianity at the expense of all citizens.