Tusla has spent nearly €3.6 million on sending children abroad for specialist residential care in the past two years.
At the end of 2020, this involved just three children.
Tusla says the majority of children are cared for in family settings, whether with relatives or foster carers.
It says there are a small number who need specialised residential care, due to their life experiences.
The agency says the majority of these are accommodated in Ireland, but a small number are sent abroad if the care they need isn't available here.
Tusla spent over €1.3 million on specialist residential care for children in the UK last year, and over €2.2 million in 2019.
At the end of last year, three Irish children were in these facilities, and nine at the same point in 2019.
Tanya Ward, from the Children's Rights Alliance, says the practice should end.
She said: "We have heard from children and young people and the families affected - and this hasn't always been a very positive effect on their lives.
"For the families affected, for example, it means they have to travel to the UK to visit their children.
"This can be very expensive, and it can also mean they don't get to see their children all that often."
She said Ireland should be looking at developing those therapies and supports here.
Tusla says out-of-state placements are only considered when the needs of the young person can't be met in Ireland.