The goal of the visit to McAllen, Texas, was "to take part in briefings and tours at a nonprofit social services center for children who have entered the United States illegally and a customs and border patrol processing center", according to a statement released by the White House.
President Trump is holding a meeting with Cabinet officials at the White House on Thursday, a day after signing an executive order to end the administration's policy of separating children from families being prosecuted for crossing the USA border illegally.
The House of Representatives will vote on a Republican immigration bill aimed at halting the taking of immigrant children from parents being detained for illegally entering the US.
"She believes we need to be a country that follows all laws, but also a country that governs with heart".
"It is unclear whether the children being separated from their families are being treated as unaccompanied minors", Durkan said.
The announcement Thursday implies that Border Patrol will hold onto the children until their parents return from court proceedings and then send them to detention together.
Senate Republicans, fearing Trump's action will not withstand a legal challenge and eager to go on record opposing the administration's policy, have unveiled their own legislation to keep detained immigrant families together.
The political compromise the first lady had sought so far has not materialized.
"I'm glad I'm here and I'm looking forward to seeing the children", Melania Trump said at a roundtable discussion with social workers and government officials. She said the executive order is a small step in the right direction but a lot of work is needed. She shook hands with children and asked kids where they were from and how long they'd been there.
The rejected bill would have curbed legal immigration and bolstered border security but would not have granted a pathway to citizenship to "Dreamers" who arrived in the country illegally as children.
The New York Times reported that though the order has been made, there were still no plans for the reunion of the children who have already been separated from their families.
'We don't like to see families separated.
The surprise trip "was 100 percent her idea", Melania Trump's spokeswoman Stephanie Grisham told reporters travelling with her to Texas.
Trump is defending his Wednesday executive order to end new family separations at the border, but says Congress needs to act to permanently fix the problem.
This week, President Trump signed an executive order reversing the policy after days of double talk from administration officials and the President himself.
From March to May this year, more than 50,000 people a month were apprehended for illegally crossing the border from Mexico.
Thursday's uncertainty resulted from the abrupt ending Wednesday of a White House-sanctioned practice of separating more than 2,300 children from their parents over the past several weeks.