The children were playing last evening behind their houses, located near the water pit, in Gorkha village, Sultanganj police station's assistant sub inspector Brijbihari Tiwari said.
When the minors, aged 5 to 6, did not return to their homes, their parents started searching for them, he said.
The family members later found the children's bodies floating on water in the pit, Tiwari said.
The police later sent the bodies for postmortem, he said, adding that a case was registered in this connection.