Rachel Henry, 22, was charged on Tuesday with three counts of murder after the bodies of her children - aged three, one and seven months - were found inside their Phoenix, Arizona home.

Two toddlers tried to fight back against their mother by kicking and punching her before she allegedly smothered them to death.

Rachel Henry, 22, was charged on Tuesday with three counts of murder after the bodies of her children - aged three, one and seven months - were found inside their Phoenix, Arizona home.

Police said her two elder children tried to fight her off in the moments before they were all smothered.

Henry allegedly told police that she started with her one-year-old daughter by holding her hands over the girl's nose and mouth until she stopped moving on Monday night.

The girl was initially kicking out at her mother while she was being smothered.

Her three-year-old brother was screaming 'no' as he watched his little sister die and repeatedly tried to punch his mother to no avail.

Henry told police that she left the girl's body at the back of the house and chased her son around until two relatives - including the children's father and another adult relative - arrived at the property.

She caught the boy and took him upstairs on the pretense of putting him to bed as the relatives sat in the living room.

Investigators say the boy pinched and scratched his mother but was unable to save himself.

She then went to find her seven-month-old daughter, gave her a bottle to feed on until she fell asleep, then smothered her as well, authorities say.

A probable cause statement filed in court by police and later made public said Henry (center) had admitted to deliberately smothering each child - two girls, aged seven months and a year, and a three-year-old boy - starting with the older daughter

Henry said she sung lullabies to all three children while they were dying.

She then propped all three bodies on the couch 'as if they were sleeping'.

Police were called to the property some time later to reports of unspecified 'trouble'.

Officers said they were called by one of Henry's relatives.

Authorities offered no possible motive for the killings but court records cited one of the other adults in the house as having told police that Henry 'had a methamphetamine addiction and had been acting strange the past several days'.

It was also reported earlier on Tuesday that the children had previously been removed from their family home because Henry's alleged addiction.

Henry, pictured holding a young child in 2013, placed all three children 'on the living room couch as if they were taking a nap' without telling either of the two other adults in the house what had happened

Henry recounted smothered her three-year-old, straddling him on the floor of a bedroom as she sang to the child

A representative from the Maricopa County Attorney's Office said late Tuesday that Henry apparently admitted to having a history of addiction to methamphetamine and that her children were previously removed from her care, according to AZ Central.

Authorities said the alleged drug abuse likely occurred in Oklahoma because the Arizona Department of Child Safety said it had no previous contacts with Henry.

The family moved to Arizona over the summer from Oklahoma.

Video shot by AZ Family showed Henry dressed in a white Hazmat suit with her hands restrained behind her back, being brought to the 4th Avenue Jail, where she is being held without bond.

Henry said nothing in response to questions from reporters asking her to address her children's deaths.

Henry was arrested and charged with murder Tuesday (she is pictured in jail uniform)

A makeshift memorial is set up near a home where Henry was arrested on suspicion of killing her three children after they were found dead inside the family home

Responding officers found the three children dead in the living room, authorities said. The children were unresponsive and were pronounced dead after officers administered CPR and firefighters provided first aid

Police were called to this address on East Vineyard Road after getting a report from one of the parents signaling 'unknown trouble'

Those who knew Henry while she lived in the town of Prague, Oklahoma, said she was a pleasant woman who they trusted to look after their own children.

Anthony Repsher, whose wife Tiffani Hardy features in photos with Henry, said he had known her for around six years.

Speaking to Fox10, he said Henry would be the last person he would suspect of harming her own children.

'As a matter of fact, she'd even babysit my children. I've never noticed any kind of depression or anger or hostility towards children or anyone else.'

Henry initially claimed an illness may have been a factor because the youngsters had been sick earlier in the night.

According to reports, officers first received an 'unknown trouble call' from one of the parents and when police arrived at the home, they were greeted by three adults.

The 30-year-old father and a 49-year-old relative identified in redacted court records as the homeowner and an aunt were also taken in for questioning.

A neighbor told local reporters he went outside after hearing a helicopter above the residential area.

Officers arrived at the scene in Phoenix, Arizona, on Monday evening and found the three young children unresponsive

Henry initially claimed an illness may have been a factor because the youngsters had been sick earlier in the night

Neighbors said the property where the children were found appeared to be a landscaping business, with trucks often arriving and leaving. Pictured (above) police at the scene Monday

David Ware said the property where the children were found included a landscaping business or plant nursery, with trucks often coming in and out.

He told AZ Central: 'I've always just assumed it was an active business. I've never seen children on the property.'

Ware said that 'cops went frantic' at the scene, adding: 'I freak out, you panic. You want to make sure there's not a present danger to your children.'

Sgt Fortune described the scene that first responders found as 'very difficult'.

First responders who tried to save the children's lives were sent home early after the traumatic event.

The family lives in a neighborhood with old homes of wood or stucco, where a white Spanish-style church graces a corner.

But there is new construction going up all around, with a golf course and several housing developments of single-family homes priced at more than $500,000.

Court records showed that Henry is being held in lieu of bail of $3million.

It was not immediately clear if Henry had an attorney. Her next court date is scheduled for January 31.