The drum belonged to the industrial unit and even hours after the police and the area MLA visited the spot today, it had not been removed. Police said the unit's proprietor, R K Jain, was missing.

Neighbours say the elder child, Somvati, fell into the drum when she tried to rescue her brother, Rajesh, who had screamed after falling in. A truck driver sleeping in a room nearby also woke up on hearing the screams and took the children out.

While Rajesh died in LNJP hospital with 40 per cent burns in the evening, Somvati died on Thursday suffering 25 per cent burns. ACP (East) S M Bhaskar said the deaths had occurred more due to the intake of chemicals rather than burn injuries.The drum contained not pure acid but chemical wastes from the unit, he added.

Police arrived at the spot only on Thursday though people living in the area said they had informed them on Wednesday itself. However, additional SHO Makesh Kumar said they were officially informed today and no one knew of the incident the previous day.

The sub-inspector who got the call and the duty officer have been placed under suspension. Police sources say after receiving the call, the cops could not locate the hospital where the dead children were as cops got no information from the hospital as is normal. A probe has been ordered into why the hospital did not inform the police, DCP Balaji Srivastav said.

The acid was so potent that the hands of the children's mother, Lachmi, got burnt when she picked up her kids. The youngest of Lachmi's three surviving daughters also sustained burn injuries on her cheek.

``I had lunch with my children before I left for work,'' said Ram Saroop, the children's father. ``But half an hourlater they were dead.''

``I had asked Lachmi not to send them out. But the children went out to play,'' he added, rubbing his hands as he sat helplessly at the Trilokpuri police station. The charred bodies, awaiting transportation to the Sabzi Mandi mortuary, had been kept in a police van there.