The incident occurred at Ambala City when the children, identified as Bittu (8) and Suraj (10), residents of a slum colony, were crossing the drain, police sources said.
The parents of Bittu and Suraj work as labourers here and hail from Bihar.
The rescue operation started nearly an hour after the incident. Employees of municipal council and fire department fished out the children after three hours.
The children were rushed to civil hospital where they were declared brought dead.