We are attending Rockville Science Day, put on the Rockville Science Center. There are around 100 registered exhibitors.
This is their description:
Come and join us at Montgomery College for the 28th annual Rockville Science Day, featuring a variety of science and technology-related exhibits, activities, games and demos. Activities and exhibits include rocket-building (and launching), telescope viewing, a travelling planetarium, all kinds of robots, backyard wildlife, ship models, microscopes, snakes, oyster farming, botball, stream science, a pigeon release, Civil War medical practice, coding challenges, math puzzles, chemistry in action (flames, explosions & other reactions), electric vehicle demos, quadcopters, archeaology mini-digs, 3D printing, and brain games.
More details: http://rockvillesciencecenter.org/rockville-science-day/