Raluca Tagani, 29, has been charged with the murder of her eight-month-old son and attempted murder of her daughter, two.
She is due to appear before Belfast Magistrates' Court later today.
Police Service Northern Ireland said in a tweet early on Friday morning that a 29-year-old woman had been charged with baby Liam's murder, and with the attempted murder of another young child.
PSNI's Detective Chief Inspector Chris Millar said in a tweet: 'The other young child injured during this incident remains in hospital where her condition is described as stable.'
He went on: 'I would like to thank the local community for their unwavering support and patience while we continue our investigation into the tragic events of Tuesday evening and I continue to ask that anyone who has any information to contact us.'
Earier Liam's tearful father attended a vigil in his honour after the baby's mother was held by police on suspicion of murder.
Liam O'Keefe, the father of baby Liam, travelled from England to Northern Ireland after the horrific attack which also left the newborn's two-year-old's sister in a critical condition, but she is now stable in hospital.
Speaking to residents at the vigil on Thursday in the blue balloon-filled street, Liam said he was 'truly heartbroken' as he thanked the community for their support.
He said, according to Belfast Live: 'To all the neighbours and the full community for all their help and support, I really appreciate it all.
'Holding this vigil means the world to me. I am truly heartbroken but it gives me the strength to know you are all giving so much love and support.
'Thank you from the bottom of my heart.'
A local priest also offered up prayers outside the Brompton Park home to baby Liam and his sister.
Tagani, originally from Romania, was also taken to hospital after the alleged attack but police confirmed yesterday she had beenreleased into police custody for questioning.
Liam's daughter from a previous relationship, Lara O'Keefe, 26, has revealed the moment they discovered about the tragedy while in England.
She said: 'When he found out that Liam had died he dropped the phone and just screamed.
'I held him as he was crying. The police and ambulance came to check how he was. My dad's a big man and he never displays his feelings. To see him like that was just horrific.
'I rang the police straight away. He flew back to Northern Ireland as soon as he could.
'He is in bits. He's had to go and see the baby's body today. His kids are his world. He is completely devastated.'
Liam O'Keefe (centre), father of baby Liam, speaks to local residents as they take part in a vigil and balloon launch at Brompton Park, Ardoyn
Speaking to residents at the vigil on Thursday in the blue balloon-filled street, Liam said he was 'truly heartbroken'
Raluca Tagani, 29, has been charged with murder after allegedly stabbing her son to death
Liam O'Keefe, who was just eight weeks old, was found dead in a house in the Northern Irish capital on Tuesday night
Relatives of little Liam have paid tribute to their 'beautiful angel' after he lost his life in the horrific attack
Tagani (pictured), originally from Romania, was also taken to hospital after the alleged attack but police confirmed yesterday she was released into police custody for questioning
A local priest also offered up prayers outside the Brompton Park home to baby Liam and his sister
William was previously married with four children before meeting Raluca in Romania while on a holiday with friends three years ago.
She since moved to Northern Ireland to be with him and had their two children together.
Ms O'Keefe said of her half-sister who is recovering in hospital: 'She was always so bubbly and happy. I can't imagine anyone harming her.
'She was just a happy little girl, she loved playing peek-a-boo. The first moment she him in hospital saw my dad she started crying and was so happy to see him.'
On Liam, she added: 'I only met him through FaceTime but he was a beautiful baby. We were planning to go over and see him. There was supposed to be a Christening. Now it will be a funeral.
'We have just got so many questions. I just can't understand it.'
Other relatives of little Liam have paid tribute to their 'beautiful angel' after he lost his life in the horrific attack.
One relative sent their prayers for 'our beautiful cousin who is fighting for her life in ICU', The Sun reported.
She went on to urge people not to speculate on what happened to let 'our whole family circle grieve.'
Another loved one said: 'The family is all heartbroken.'
Police and medics rushed to the house earlier this week, but sadly Liam could not be saved and was declared dead at the scene.
The Police Service of Northern Ireland (PSNI) have launched an investigation into what is understood to have been a domestic stabbing incident in Brompton Park.
Floral tributes and teddy bears have been left outside the front garden, which still has a baby's pram and doll on it.
A 29-year-old woman has been arrested on suspicion of murder after an eight-week-old baby was reportedly stabbed to death and another was left serious injuries at a house in Belfast
Scene at Brompton Park in north Belfast where police have launched a murder investigation
Sinn Fein North Belfast MP John Finucane visited the scene on Wednesday.
He said: 'It was a very tragic situation which unfolded here in Ardoyne last night.
'It is my understanding that first responders entered a house, they found two young children very seriously injured and despite their best efforts one child died at the scene.
'Another child has been taken to hospital and is currently in a critical condition.
'Our hopes and prayers are that that child will pull through and make a full recovery.
'Police have arrested a 29-year-old woman, they have commenced a murder investigation also so I think that process has to take its own course.
Police forensics officers pictured at the scene and there is a large police presence in the area
'Everybody in the community, their thoughts are with the families that are directly affected by this.
'It is a tragic situation compounded by the fact that we are dealing with somebody who has died at such a young age.'
Mr Finucane added: 'I think there is a senselessness to it, I think people find it very difficult to try to comprehend the facts as they are being relayed and the facts as they are emerging.
'It is incredibly difficult and will obviously leave a mark on those who are most impacted by it, and all we can do is rally round those who need support at this time.
'This has been hugely impactful.
'There were neighbours who assisted and some people who would have witnessed scenes that they shouldn't have to witness.
'Ardoyne is a very proud community, it is a resilient community also and I have no doubt whatsoever that they will rally around each other at this very difficult time, they will provide help and assistance for those who need it.
'I would also just stress just for people to exercise caution and sensitivity in regards to what they would post or share on social media, there is a live murder investigation and people need to be respectful of that process as well.'
Police Service of Northern Ireland say a 29-year-old woman is in custody for questioning
A Police Service of Northern Ireland have said they are not looking for anyone else in connection to the incident.
Det Ch Insp Millar from the Police Service of Northern Ireland's Major Investigation Team said: 'Police were called to the house shortly after 8pm last night and discovered the injured baby and another injured child in the house.
'Despite the efforts of the emergency services the baby was sadly pronounced dead at the scene. The other young child was taken to hospital and remains in intensive care.
'A 29-year-old woman who was also in the house has been arrested on suspicion of murder and attempted murder and remains in custody at this time.
Ambulance crews had earlier taken the two children to hospital following what is understood to have been a domestic stabbing incident at a home in Brompton Park in Belfast (pictured)
'Our thoughts are with the baby's family, who are being supported by Family Liaison Officers.
'While our investigation is at any early stage I can confirm that at this stage, we are not looking for anyone else in relation to this tragic death.
'I would like to thank the local community for the support that they have provided and would appeal to anyone with any information that can assist our investigation to contact us on 101 quoting reference number 1787 27/07/21.'
SDLP deputy leader and North Belfast MLA Nichola Mallon said the local community was in shock.
The scene in the Ardoyne area of north Belfast where police have launched a murder probe
'It is important that the PSNI are given the space and full co-operation to fully investigate this terrible incident,' she said.
The Northern Ireland Ambulance Service received a 999 call at 8.16pm on Tuesday.
A rapid response paramedic and two emergency crews attended.
People Before Profit councillor Fiona Ferguson said the news was 'truly devastating'.
'A wave of shock began in Brompton Park last night and spread out across north Belfast,' she said.
'After something so shocking, community solidarity, community support, rallying around each other is going to be absolutely paramount.'
A post-mortem examination on the boy is set to take place today.