The U.S. Secret Service ordered hundreds of parents and their cancer-stricken children out of Lafayette Square on Saturday night, barricading the park for at least two hours and disrupting the group’s plans for a candlelight vigil to raise awareness and research funding for childhood cancer, participants said. Some of the parents and children expressed hurt and disappointment that the Secret Service and Park Police, citing security precautions, virtually shut down part of a two-day event called CureFest for Childhood Cancer. “We ended up waiting at the gates for two hours, and they never let us in,” said Natasha Gould, an...