Tusla has confirmed that it had dealings five years ago with the child in Donabate, north Co Dublin, who is now missing and presumed dead, and his family.
The Child and Family Agency said in a statement that their engagement with the family and the child ceased in 2020.
The child would have been two years old at the time.
Since Tusla ceased its engagement, the child disappeared, and gardaí believe he is dead.
They are searching an area of wasteland in Donabate for his remains.
A cadaver dog was brought on site to search for the boy's remains and the garda helicopter was in the air taking aerial photographs.
A section of the wasteland has been taped off inside the cordon - an area of the search site gardaí seem particularly interested in.
Tusla said the family requested their services, but these ceased in 2020.
They did not say why these services ceased, or why no further checks or contacts appear to have been made after the child was two years old.
He would have been seven years old now.
Tusla also said that since 2020 no new referral or information of concern was received about this child until last Friday, when they referred the matter to gardaí following a report from the Department of Social Protection.
The Child and Family Agency said it is issuing this statement in the interests of openness and transparency and is now conducting a review of its engagement with the family which is to be sent to the National Review Panel.
It also said it will not be providing any further detail of their involvement with the child or his family because of the ongoing garda investigation.
It is the second missing child case that Tusla has been involved in as it also had dealings with Kyran Durnin and his family before the Co Louth boy went missing.
He is also presumed dead and is the focus of an active garda investigation.
Tusla chief executive Kate Duggan previously described the case to an Oireachtas Committee as "absolutely horrific" and said the Child and Family Agency has completed two reports reviewing any involvement it had with the case.
She said these have been passed on to Minister for Children Norma Foley and would be published "once the live investigation is over".
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Earlier, the Garda Commissioner said the search for a boy has so far been unsuccessful.
Justin Kelly, who took up the role this week, said investigators have been unable to identify any information on the boy's current whereabouts or evidence as to whether he is alive.
Speaking at a press conference, he said: "Tragically, investigating gardaí believe the boy is deceased."
Gardaí said they are investigating all of the circumstances around the disappearance and whereabouts of the boy who would be seven years old if still alive.
Concerns for the boy were raised by the Child and Family Agency and reported to gardaí on Friday.
A garda statement said: "The boy is last known to have resided at The Gallery Apartments, Donabate, Co Dublin.
Watch: Garda Commissioner Justin Kelly provides update on investigation
"It has been a number of years since there has been any confirmed sighting of the boy, who would now be seven years of age."
Yesterday, gardaí took control of an area of open ground in Donabate, which will be the subject of a search in the coming days.
Mr Kelly also appealed for anyone with information on the missing boy to contact investigating gardaí.
He said a senior investigating officer had been appointed and added: "All resources are being deployed."
The child, a boy who would now be seven years old, has not been seen for at least three years, when he was around three-and-a-half years old.
The search, which involves excavation equipment and includes the Garda Technical Bureau, is to continue in Donabate for a number of days.
The scene on the Portrane Road was sealed off last night and gardaí have asked for time and space to enable them to conduct the search operation sensitively.
The perimeter of the site, which is largely overgrown, has been fenced in and areas covered with black fabric.
Gardaí have brought in excavation equipment, lighting and generators and forensic specialists from the Garda Technical Bureau are at the scene.
Three entrances to the site have also been sealed off.
The location was identified from information received in the investigation into the disappearance of the child.
Gardaí have already carried out searches and a technical examination at an apartment in the Gallery Apartments in Donabate, the place where the boy is last known to have lived.
Detectives have so far been unable to either locate the child, identify any information on his current whereabouts or find any evidence that he is currently alive.
They suspect he may have come to some harm but do not know if that was accidental, intentional, violent or criminal.
They say they are keeping an open mind, including to the possibility that the child died of natural causes, and say they are handling this case sensitively.
Minister for Children Norma Foley has said she is deeply concerned for the welfare of the child.
Tusla has described it as "a sensitive case".
The case came to light last week after the Department of Social Protection raised concerns with Tusla following an application for social welfare.
The application, which was made for child benefit in the name of the child, was examined and the department carried out inquiries.
The department then discovered that there was no record of the child having ever gone to school.
Gardaí carried out searches and a technical examination at the apartment in Donabate over the weekend.
They are searching for the remains of the child which if discovered, could help establish a cause of death.
Gardaí say they have not ruled out any possibility, from homicide to natural causes or accidental death.
They have spoken to the child’s parents and wider family members, some of whom are abroad, as part of the investigation.
They also say they are not in a position to identify the boy or his family at this time "for operational reasons".
No arrests have been made.
Gardaí have issued an appeal for anyone with information to contact the incident room at Swords Garda Station.
They have also requested the media to provide them with the space and time to carry out this search operation sensitively.
CEO of Children's Rights Alliance expresses shock at case
The CEO of the Children's Rights Alliance has expressed her shock at the case.
Speaking on RTÉ's Morning Ireland programme, Tanya Ward said she had to read the story twice in order to believe it, particularly "because of the similarities of the Kyran Durnin case and it's absolutely shocking to hear that something like this has happened".
Kyran Durnin was reported missing from his home in Drogheda, Co Louth, a year ago. Gardaí are working on the assumption that Kyran, who would now be nine years old, is missing presumed dead and that he may have died up to three years ago.
Regarding the missing boy in Donabate, Ms Ward pointed out that the child's age range means he may have fallen through the cracks as a result of Covid and the absence of contact with frontline staff and family during the lockdown periods.
However, she added there are a range of people including public health nurses and GPs that could have been in contact with the family over the years.
"I do wonder about the role of Covid, but ... there's public health nurses, there's GPs, there's early year services he may have been in contact with. And I'm thinking about: Did anyone see anything? Did anyone intervene? Is there something that could have been done to help this child early in his life?"
Ms Ward said it is terrifying for those working in the child protection sector that something like this could have happened to a small child.
Meanwhile, Ireland's Special Rapporteur on Child Protection has said that the case of the missing boy in Dublin is horrifying and heartbreaking and she understands the public concern about how this could happen to a young child.
However, Caoilfhionn Gallagher stressed there are some "very definite differences" between this case and that of Kyran Durnin.
Speaking on RTÉ's Today with Claire Byrne, Ms Gallagher added that Tusla responded quickly as soon as concerns were raised.
She said that there are real questions to be asked about whether there are enough robust systems in place for ensuring that vulnerable children are kept on the radar.
Ms Gallagher explained that there were far more concerns about Kyran's case because he was a primary school pupil and on the radar of social services.
But, she added, there must be better structures in place to ensure that all children are protected.
"I think there are real questions about whether at any stage, including pre-schoolers, but also including children who are post compulsory school age, whether we need to have better systems in place for ensuring that vulnerable children, children who may be at risk, are on the radar."
Additional reporting: PA
