Trump had initially responded to criticisms by claiming that it was not in his power to reverse the family separation policy, which his own administration had implemented.
Moore, who has been photographing the American migrant crisis for more than a decade, was tagging along with USA border patrol agents who were waiting for a group of Honduran migrants to cross the border.
"As a father myself, it was very hard for me to see these families detained, knowing that they would soon be split up", Moore told Getty's blog Foto.
A two-year-old Honduran asylum seeker cries as her mother is searched and detained near the U.S. -Mexico border on June 12, 2018 in McAllen, Texas.
US House of Representatives to vote on immigration bill
The first lady met with officials and employees at the facility, where 55 children aged 12 to 17 are housed. Third-graders welcomed the first lady with a large paper American flag they'd signed taped to a wall.
Time Magazine's latest cover takes a shot at US President Donald Trump's border family-separation policy, one week after Trump wondered if he would be on the magazine's cover after the North Korea summit in Singapore. "But then it was over and they drove away." he said, adding that he wanted to stop her crying.
The new cover features an iconic photo captured by Getty Images Pulitzer Prize-winning photograhper John Moore. "It was a moonless night", Moore told NPR in a recent interview. However, the order did not specify any solution for the 2,300 children who are reportedly being detained or bounced around the country without the parents who crossed the border with them.
The new Trump administration policy, which went into effect in May, sought to maximise criminal prosecutions of people caught trying to enter the U.S. illegally.
The House will vote Thursday on two immigration proposals. Federal agents asked the mother to put down her child so they could body search her. Since Attorney-General Jeff Sessions announced the policy, almost 2,000 children have been taken away from their parents.