This family-friendly weekend event is jam-packed with tours and workshops for museumgoers. Saturday, kids ages 8 to 12 can take part in the workshop Planning Urgan Places and Spaces (10am), introducing them to how urban planners think about transportation, or one that has them learning about urban planning principles, then designing their own city block (noon). Sunday's workshop, the Greatest Grid (10am, noon; ages 6 to 12), tours kids through the blockbuster exhibit "The Greatest Grid: The Master Plan of Manhattan," and has them plan the streets and buildings of New York City's future. Free ice cream (while supplies last) and docent-led tours (Sat noon, 2, 4pm; Sun 2, 4pm) round out the weekend's offerings. All ages.