The workers began the strike on Monday morning saying management has failed to show any interest in returning to the bargaining table.
The Ontario Public Service Employees Union says negotiations broke down on the weekend.
The union says key concerns at the table were workload, job security, hours of work and layoff language.
OPSEU says managers ordered staff to turn in their laptop computers and office keys last Friday.
OPSEU represents frontline social workers, child-protection workers and accountants serving 4,300 children in the Peterborough area.