With countless miles swamped by the floods, nobody knows when the searches will end.

Several hundred people gathered at Tivy High School’s stadium in Kerr County, Texas, to mourn the victims of the catastrophic flash floods that hit the region and to honor the many still missing.

Henry DeHart, interim president and CEO of the American Camp Association, said counselors typically receive training in areas such as risk management, emergency procedures, child development, abuse pr...