Plymouth County prosecutors have opened up an investigation into the circumstances that led a 2-year-old Brockton boy to become “unresponsive’’ Monday evening. He remained hospitalized with serious injuries as of Thursday afternoon.

Beth Stone, a spokeswoman for the Plymouth District Attorney’s office said the child was taken from a home on East Main Street and flown to Massachusetts General Hospital.

Brockton police Lieutenant William Hallisey said Thursday that the detective unit was involved in the case, and that he had not yet heard any update on the condition of the child.

A spokesman for the Department of Children and Families, which is required to be notified of any child injuries in which abuse or neglect is suspected, acknowledged that the agency has “received a report and we are investigating.’’ She also said that the agency had no previous history with this family and no other children live in the home.