Joaquin Phoenix and Rooney Mara feel the pain of migrant parents split from their children now they are parents themselves.

Joaquin Phoenix and Rooney Mara

Joaquin Phoenix and Rooney Mara

The 'Joker' star and the 'Girl With The Dragon Tattoo' actress penned an op-ed essay about the migrant children, whose parents can't be found, as they spoke about parenthood and the devastating thought of being away from their own child.

They wrote: "Like many, we were pained to realise 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. 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. As Americans, it’s our responsibility to continue paying attention to the plight of these families and get answers for why they still have not been located."

Joaquin and Rooney - who welcomed son River into the world in September - were speaking out to urge the United States to continue to look for the parents of the 545 children who were separated by immigration officers at the country's border.

In their essay for People magazine, they added: "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? 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."

In September, director Viktor Kossakovsky confirmed Joaquin was not able to promote his film 'Gunda' because he "just got a baby", and the pair named the little boy after River Phoenix, who died in 1993 aged 23 of combined drug intoxication.

Speaking at the Zurich Film Festival, Viktor said: "He just got a baby, by the way, his name was ... a beautiful son called River, so he cannot promote it [the film] now."