It's Brooklyn-Queens Day (aka Anniversary Day)

Besides being Thursday, today is Brooklyn-Queens Day, which is also known as Anniversary Day, and NYC public school children have the day off (that's why you may see more kids than usual). The day originally celebrated the founding of the first Sunday School on Long Island. Really.
According to the Queens Public Library:

Brooklyn-Queens Day originated as a Protestant holiday celebrated in the City of Brooklyn in 1829. Back then it was known, and fondly remembered by some, as Anniversary Day. Anniversary Day is celebrated annually on the first Thursday in June, commemorating the founding of the First Sunday School on Long Island. The first parade was held in Brooklyn June 1829. The New York State Legislature enacted, in 1959 at the request of the Queens Federation of Churches, the bill permitting the schools in both Kings and Queens Counties to be closed on this day. It was signed by Governor Nelson A. Rockefeller.

Now all students in all NYC counties get the day off, while their teachers must endure Chancellor's Conference Day. Teacher "Miss Eyre" at NYC Educator thinks about her students, "My dollbabies will undoubtedly be celebrating by sleeping late; catching up on Degrassi, Maury Povich, and Call of Duty: Modern Warfare; and, I hope to God, finishing their social studies exit projects. Somehow I doubt that any of them will be commemorating the vital role that Sunday School, Brooklyn, or Queens has played in their lives. I suppose that's all right. If I were at home, I probably wouldn't be doing any of those things either."