Heritage India Festival at the Dulles Expo Center celebrates South Asian culture with entertainment, cuisine and commerce. Kids under 5 are free: http://www.hifestival.com
Greenbelt Green Man Festival isa family-friendly event celebrating the commitment to preserve the forest with activities that reconnect to folklore of ancient civilizations through science, music, art and more.
Super Science Saturday at the Hazy Center in Chantilly presents an energy series. Visitors of all ages will be immersed in science, technology and aviation with hands-on activities, demonstrations and go-cart cars built by high school students: http://airandspace.si.edu/events/detail.cfm?id=9702