Joaquin Phoenix and Rooney Mara have publicly spoken about their baby boy, River, for the first time.

Russian filmmaker Victor Kossakovsky revealed that the actors welcomed their first child together back in September.

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Now the new parents have opened up about their son in a new op-ed about the 545 migrant children who were separated from their parents by U.S. immigration officers.

The essay, which was published exclusively in People, begins, “Last week, we learned that the parents of 545 children separated at the border by immigration officers have not yet been found. The weight of that number is staggering. Five hundred forty-five children.”

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Like many, we were pained to realize that despite falling out of the headlines, the policy of family separation continues to damage children and parents across the world, more than two years after it was ruled illegal by a federal judge.”

Speaking about how the situation has emotionally impacted them as new parents, the activists continue, “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.”

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To conclude the op-ed, Phoenix and Mara consider how they will explain this situation to their son when he is older: “We have to ask ourselves: ‘Is this the country that we want? Are these our values? How will it feel to explain to our son, when he asks us about this time and how we treated scared, defenseless children, some of whom may never see their parents again?'”

Adding, “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.”