Rooney Mara and Joaquin Phoenix

Earlier this year, Joaquin Phoenix and Rooney Mara welcomed their first child, a baby boy they named River. Now, for the first time, the actors have opened up about their son.

In an emotional op-ed for People magazine about the current migrant crisis in the United States, the couple mentioned their baby while addressing the 545 children whose parents cannot be located after they were separated from their families at the border by immigration officers.

Mara and Phoenix wrote, “As new parents, it’s unbearable to imagine what it would feel like to have our child taken away from us for a day, let alone years. But that’s the very situation those 545 children and their parents have been living through.”

The couple continued, “For the children who remain separated from their parents, the damage will be lifelong. Child psychologists say that even short periods of forced removal from the care of a parent can cause irreparable emotional harm. Some of these children are no more than toddlers or have yet to reach their 10th birthday. Our hearts break to think about the suffering they’ve endured at our country’s hands.”

Phoenix and Mara subsequently called upon readers to demand justice for the hundreds of children who remain separated from their parents. “For the sake of our nation’s character, I hope we will be able to tell him that America unequivocally rejected this cruelty and demanded that our representatives did everything in their power to find those missing parents,” the couple wrote.

This article originally appeared on Harper’s BAZAAR US.