WASHINGTON — The head of the Secret Service apologized for how a group of children suffering from cancer and their families were treated after they said they were pushed out of Lafayette Square on Saturday night.

Joseph Clancy, director of the Secret Service, called one of the organizers Monday after CureFest for Childhood Cancer said that about 700 parents and children were ordered out of the park in front of the White House for at least two hours. The move disrupted their plans for a candlelight vigil to raise awareness and research funding for childhood cancer.

Closures of Lafayette Square have occurred periodically since the attacks of Sept. 11, 2001, and during security incidents at the White House.