Tusla's decision to return two children to their family amid serious abuse allegations will come under the spotlight today.

The Child and Family Agency has been ordered to appear before a High Court judge to explain the reasoning behind its decision.

The children were taken into care in 2012 over concerns about parental neglect, violence and substance abuse.

They were aged 2 and 4 at the time and their two older siblings were also taken in.

Their foster parents noted they displayed highly sexualised behaviour, but it would be two years later before their older brother made certain claims to Gardai.

Following a 29 day hearing last May, Tusla withdrew an application for orders to keep the children in care.

This paved the way for them to be returned to their natural parents but that was put on hold because of the intervention of their foster parents.

A temporary order preventing their return is in place to apply for a full hearing to take place before the High Court today.