Local students between 6 and 14 years old, along with children from military families, were invited to trick-or-treat their way across the North Lawn.
No tricks are scheduled, but participants will receive treats: a box of White House M&Ms, a sweet dough butter cookie made by pastry chef Bill Yosses, and dried fruit.
During the festivities, the children can meet spooky costumed characters, including Dracula and Frankenstein, and watch a pumpkin-carving demonstration.
Later, the military families will continue the celebration inside the White House.
Late Sunday afternoon, workers were busy putting the finishing touches on the decorations as Obama returned to the White House from a campaign trip.
Multicolored pumpkins and gourds lined the driveway - individually, in gravity-defying stacks and as part of a large mound over five feet tall. Pumpkin-headed scarecrows made of cornstalks loomed over the path with menacingly raised arms. Under the White House portico, a mobile resembling bats flying through clouds fluttered around a lantern.
Some of the local children are students at Bancroft Elementary, which helps tend the first lady's White House garden, and Tubman Elementary, which has a relationship with the White House chefs.
Last year, the Obamas stood outside the White House front door chatting and passing out cellophane goody bags. The president, dressed in casual clothes, was one of the few not in costume. Mrs. Obama wore furry cat ears and a leopard-patterned top.
Over the years, the winter holidays have been the ones to get the full treatment at the White House, with Christmas trees and tinsel all around.
The Obamas are not the first, though, to show Halloween spirit.
President George H.W. Bush and first lady Barbara Bush hosted 500 children on Halloween in 1989, loading them up with fun loot but also teaching them about the dangers of drugs. In the Clintons' first year in the White House, a huge orange jack-o'-lantern was formed around the front entrance to the White House, with the front door to the mansion serving as the middle tooth.