Seven persons, including five children, were killed and 12 others injured when a bomb planted by Maoists went off at Pachokhar village in Bihar's Aurangabad district Sunday morning.Superintendent of Police Vivek Raj Singh said the bomb, planted by the Maoists, was found by the security personnel on Saturday during the sixth and final phase of elections. However, police left the bomb in a field for follow up action to defuse it. As the villagers went to the field Sunday morning, the bomb suddenly exploded killing seven persons including five children on the spot.Twelve people, who sustained splinter injuries, were admitted to hospitals in Deo and Aurangabad towns. The condition of five of them is stated to be critical.