Had two children found dead in a flat been plied with strong lager?

The boy aged five and his baby sister were discovered after police were called to an incident involving their drunken mother in a nearby street.

Scroll down for more...

A bus driver was concerned about the behaviour of the woman and her partner towards another girl, aged three, believed to be the woman's elder daughter.

The youngster was being given alcohol, thought to be strong lager, by the pair, who were both drunk. The child was so intoxicated that she could hardly stand up.

Police arrested the 25-year-old woman and her 62-year-old companion, and went to their home in Melfort Road in Thornton Heath, south London, where they discovered the children's bodies.

Detectives believe the children died as a result of prolonged neglect. They do not know how long they had been dead.

They are expected to begin a murder inquiry today after a post-mortem examination of the bodies has been conducted.

A source close to the case said: "We believe the dead children may have been plied with alcohol, but are awaiting formal confirmation of this."

Last night the children's mother was sectioned under the Mental Health Act while her partner was released on police bail.

Child abuse investigators were trying to establish whether the family was previously known to Social Services. Croydon Council refused to comment.

The tragedy unfolded at about 9.30am on Saturday following reports that a young girl was being given alcohol in the street by a man and woman.

A female witness who did not wish to be named said all three were drunk.

She added: "The police turned up and grabbed the child and then ran. The child seemed to be their main priority.

"The little girl obviously wasn't right. She seemed so drunk she could not even stand up.

"What shocked me was the child didn't cry. She didn't make a sound. With all that going on, you would think the child would have cried."

She added: "The man looked like a tramp to me. He was filthy - really dirty. He had a grey beard and straggly hair and was wearing some sort of raincoat or overcoat."

The relationships between the adults and the children was still being investigated, police said.

Neighbours in Melfort Road, a quiet street of mixed Victorian and 1930s houses, said they thought the woman had moved in within the last six months.

William Pobie, 28, said he had seen her standing in the street on Friday afternoon behaving erratically and counting aloud passing cars.

Ben Solomon, 63, said he had not known the children even though he lived only a couple of doors away. He said neighbours were shocked and very upset by the news.

"These kids haven't even seen life yet and then this happens."

Evelyn Martin, 75, another Melfort Road resident, said: "It is a wonderful road to live in and the safest road to live in as far as I am concerned."

Speaking about the two children, she said: "As far as we know they were new residents and nobody knew them."

Superintendent Chris Bourlet, of Croydon Police, said officers were treating the deaths as a "suspicious incident".

"Clearly this is a tragic set of circumstances," he said. "Obviously there are a lot of inquiries to be done. This is an early stage in the investigation but we will find the answers."