The foster parents of two children at the centre of serious abuse allegations have asked the High Court to take responsibility for them.

It comes after Tusla withdrew an application from a lower court to keep the siblings in care amid concerns over their natural parents.

Rosario Boyle, who is representing the foster parents, opened their case this afternoon by asking Ms Justice Marie Baker to direct an inquiry into whether the children should become wards of court - a process whereby the High Court can become a protective guardian.

The brother and sister, now aged six and nine, were first taken into care in 2012 over concerns about parental neglect, domestic violence and substance abuse.

They displayed highly sexualised behaviour and an older sibling later claimed they had been exposed to sexual abuse in the family home.

Despite these allegations, Tusla paved the way for them to be reunited with their natural parents by withdrawing an application for orders to keep the children in care last May.

Ms Boyle described a meeting between a social care worker and the foster parents two months later, where they were told the decision was made at management level because it was 'too toxic and costing too much' - a claim denied by the social care worker.

They are asking for the court's protection on an "exceptional basis" amid what they claim would be an unacceptable risk if they were returned to the family home.