The bodies of two children, both under six years old, have been found at an address in south London.
The bodies of the children were found in Melfort Road in Croydon
They were discovered by police shortly after officers arrested a man, aged 60, and a woman in her 20s in Melfort Road, Thornton Heath at 0930 BST.
A girl who was with them, also aged under six, was taken into care and has been receiving hospital treatment.
The couple have been taken to south London police stations where they remain in custody.
A member of the public alerted police over concerns about the girl's treatment by the couple, a Metropolitan Police spokeswoman said.
She said police were informed that the girl was being given an alcoholic drink.
The spokeswoman said "as a result of immediate inquiries", officers went straight to a nearby address and found the two dead children.
Supt Chris Boulet, from Croydon police, said the investigation was at an early stage and it was currently an inquiry into suspicious deaths, rather than a murder inquiry.
"Clearly, this is a tragic set of circumstances and we are doing our best to investigate what has happened here and we'll be making full inquiries to find out exactly what has gone on."
A post-mortem examination is being carried out to determine how the children died.
Police would not confirm if either the man or the woman was related to any of the children involved.
Supt Boulet said: "This is a suspicious incident at the moment, obviously there are a lot of inquiries to be done, this is an early stage in the investigation, but we will find the answers."
Ben Solomon, 63, a resident of the road, 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."
Ashif Shanji, 32, from Norbury, who owns a watch shop opposite the address where the children were found, said he did not know the children, but he believed they were fairly new to the area.
"It is very disturbing and it has knocked everyone to hear about this. You do not expect anything like this to happen so close to home."