Up to 50,000 children living in border counties could be negatively impacted if there is a "no-deal" Brexit, according to the Children's Rights Alliance.
The group says it is seriously concerned about the psychological impact a potential hard border could have on them.
Tanya Ward, chief executive of the charity, says she is also worried about a hard borders impact on child poverty in the region:
"Both north and south of that border you have higher rates of child poverty and that's because there was a border for a long time," she said.
"(I'm) really worried about what a border would do for children and young people around those counties."
She also says there could be a lasting psychological impact if a hard border was re-introduced:
"Anyone who lived while the border was in operation will tell it did have a big impact in how they thought about themselves and whether they went to Northern Ireland or not. And it hasn't been there.
"So you have 50,000 children that have friends, go to school across the border every day, go shopping across the border," she said, adding that the situation was "concerning".