Officers made the grim discovery in the early hours of Sunday at a house in Merseyside.
It is believed the babies, found at a property in Harlow Close, St Helens, could have been born as long ago as the mid-1980s.
Two women and a man were questioned by police before being released pending further inquiries.
They are understood to be Bernadette Quirk, 54, and her son Christopher Quirk, 26, who live at the address, and her daughter Joanne Blackburn, 38, who lives nearby.
Neighbours said they thought the tip-off was linked to a row between women after a party nearby on Saturday night.
Police were called as the alcohol-fuelled fracas continued on to the street.
The next morning, detectives arrived at the house followed by undertakers with three small coffins.
Lyn Murphy, 44, who has been living in the street for 14 years, said: "There was a fight on the street after an Ann Summers party and the police came to break it up."
She described how officers arrived at Harlow Close at about 6am the next day and she saw the small coffins being brought into the house by undertakers and later taken away.
Ms Murphy said: "I believe the bodies were in the attic, because I heard the police making noises upstairs as they were searching the house.
The attics in these houses are very close together."
Ms Murphy said there has been plenty of police activity around the house since it was raided on Sunday.
"There have been police forensics going in and out of the house for the past few days," she added.
Merseyside Police said forensic tests were being carried out to determine the age and sex of the children.
Officers remained outside the small house on the red brick housing estate today.
The house is in a terrace of five two-storey homes, with small front and back gardens.
Detective Superintendent Steve Naylor said: "Following a call to us, we attended an address in St Helens where human remains were discovered.
"The remains are believed to be those of newborn babies and at this stage of the inquiry it is believed they are the remains of three babies.
"The investigation has only recently commenced and a number of lines of inquiry are being explored.
"We cannot speculate as to the cause or circumstances of the deaths and any inappropriate supposition is likely to have a severe impact on the investigation and the family concerned.
"This looks like being a complex investigation, and a lot of hard work needs to be done before we can ascertain what the full circumstances are surrounding this situation."