The body of 17-year-old Shane O'Connor - singer Sinéad's second-youngest child - was located in Bray 24 hours later.
Shane was under the care of the Child and Family Agency Tusla and his death will now be referred to the National Review Panel, which examines the deaths of children in care.
Last night, Sinead confirmed she has formally identified her tragic son's body as she slammed the State's handling of the case.
She wrote on Twitter: "I have now formally identified the remains of my son, Shane. May God forgive the Irish State, for I never will."
She went onto say: "Now Tusla want to discuss with me 'a media release', no doubt wishing to have me join in their efforts to make this death of my child seem like it wasn't at the hands of the Irish State."
She added: "Refusals to accept responsibility. Couched as always in the omnipotent and false concern they claim to have for the privacy of the children who die on their watch."
Writing on Twitter prior to the discovery of his body, 55-year-old singer Sinéad asked: "How has a 17-year-old traumatised young person who was on suicide watch in Tallaght Hospital's Lynn Ward been able to go missing?
"Hospital, of course, so far refusing to take any responsibility. Anything happens to my son on their watch. Lawsuits."
In a separate post, Sinéad said: "I want to know why Lynn Ward at Tallaght Hospital who were supposed to have HCAs (Health Care Assistants) supervise my child 24/7 have managed to let him out of their grasp this morning when seven days ago he made two severe suicide attempts."
According to Tallaght Hospital's website, the Lynn Ward, where Sinéad said Shane had been admitted, is a 36-bedded private ward located on Level 2 of the facility which caters for a wide variety of specialties.
Sinéad's tweets were put to the Health Service Executive (HSE) by the
Sunday World yesterday.
In a statement, a spokesperson said: "The HSE cannot comment on individual cases when to do so might reveal information in relation to identifiable individuals, breaching the ethical requirement on us to observe our duty of confidentiality."
Paying tribute to her son, Sinéad described him on her Twitter account as: "The light of my life. The lamp of my soul. My blue-eyed-baby.
"You will always be my light. We will always be together. No boundary can separate us."
Sinéad also criticised the child and family agency Tusla, saying the agency had made no contact with her in the 26 hours since her son's death.
"Twenty-six hours after my son died in the so-called care of the Irish State in the form of Tusla, I have yet to receive any contact from Tusla or their representatives.
"I was informed by Gardaí of my son's death and later I spoke with the GAL (Guardian Ad Litem). No contact from Tusla is unacceptable."
This tweet was put by email to Tusla by the
Sunday World yesterday. A spokesperson said the body does not comment in cases where a child in care dies. In such circumstances, the child's case is passed to the National Review Panel for examination.
The Review Panel, on its website, says it conducts reviews of child deaths to produce reports with a view to improving the quality of services provided.
After he was first reported missing, Sinéad issued several public appeals through her Twitter account begging him to get help.
In one she wrote: "Shane, your life is precious. God didn't chisel that beautiful smile on your beautiful face for nothing.
"My world would collapse without you. You are my heart. Please don't stop it from beating. Please don't harm yourself. Go to the gardaí and let's get you to hospital."
News that Shane had died and that his body had been found was confirmed early yesterday by gardaí.
Sinéad wrote of Shane's death: "My beautiful son, Nevi'im Nesta Ali Shane O'Connor, the very light of my life, decided to end his earthly struggle today and is now with God. May he rest in peace and may no one follow his example. My baby I love you so much. Please be at peace."
Shane had three siblings - Jake Reynolds (33), Roisin Waters (25) and Yeshua Francis Neil Bonadio (15). Last year, Sinéad posted a poem by him, saying it was her favourite thing about 2021.
Shane's father was Dónal Lunny - one of Ireland's most admired traditional music stars, best known for his roles with Planxty, The Bothy Band, Moving Hearts
Speaking about his relationship with his children on The Late Late Show last year, Tullamore father-of-three Donal said lockdowns and the pandemic had been tough on teenagers who were missing out on pivotal parts of their adolescence.
He told Ryan Tubridy: "In Dublin, within shouting distance, I have my daughter Cora and son Shane. We don't get to see each other and we're just up and down the road, so we might as well be far away from each other. So, it's tricky."
If you have been affected by the issues raised in this article, contact the Samaritans on 116 123; Pieta House on 1800 247 247 or text HELLO to 50808, a free 24/7 text support service for people going through a mental health or emotional crisis.