Twenty people have been indicted as part of a widespread investigation into allegations of payroll and unemployment fraud involving the Boston longshoremen’s union, including five workers who put children as young as 2 on the payroll, prosecutors said Wednesday.

Those indicted included 19 current and former longshoremen, as well as an employee of the Massachusetts Port Authority. The longshoremen worked at the Conley Container Terminal in South Boston and are members of the International Longshoremen’s Association.