Brexit will likely lead to increased child poverty and threaten loopholes in systems that protect children from abuse, campaigners have warned.
The Children's Rights Alliance (CRA) has told an Oireachtas committee that Britain's decision to pull out of the EU could also hit children's access to critical services in Ireland.
Tanya Ward, chief executive of the group, has pleaded for Northern Ireland to be designated a special case that would allow EU protections to remain within the region and maintain crucial funding from Brussels.
"Brexit poses a significant threat to children on this island, North and South," she said.
"Likely implications include an increase to child poverty rates and the potential exploitation of loopholes in child protection systems."
Ms Ward said children on both sides of the border already have among the highest rates of child poverty in the EU - a quarter of children in Northern Ireland and 12% in the Republic live in poverty.
The economic shock from a hard Brexit would almost certainly plunge children further into poverty, she told Dublin's Joint Committee on the Implementation of the Good Friday Agreement.
Furthermore, it threatens to weaken international defences against child sex abuse and exploitation, she told the committee.
There are lots of different ways that child protection systems interact between different countries within the EU and it is necessary that they do interact, Ms Ward said.
She said painstaking work is needed to ensure Brexit doesn't open loopholes for predators travelling between jurisdictions as well as for child traffickers.
Ms Ward also cautioned that any threat to dual citizenship in Northern Ireland could erode children's access to cross-border services.
"We are calling on the EU and all parties to consider Northern Ireland as a special case," she said.
"The Good Friday Agreement recognises the right of people in Northern Ireland to hold Irish citizenship. A hard Brexit cannot rob them of this right."