The Department of Homeland Security said last week that almost 2,000 immigrant children had been separated from their parents over a span of six weeks after Attorney General Jeff Sessions announced the new "zero tolerance" policy.
"Mrs Trump hates to see children separated from their families and hopes both sides of the aisle can finally come together to achieve successful immigration reform", her communications director, Stephanie Grisham, told CNN.
Hillary Clinton, speaking at a women's event in NY, said the Trump administration's "zero tolerance" policy that has separated children and parents at the southern border was a "moral and humanitarian crisis".
Van Hollen, a Democrat, called the policy of breaking up families who have entered the country illegally "cruel".
President Trump has consistently blamed Democrats for the situation, saying their support for passage of a broader immigration bill would end the separations.
Politicians and religious groups are among those to have criticised the "inhumane" policy, and the first lady - who last week returned to the public eye for the first time in nearly a month - has admitted she has found it hard to watch the events unfold. "It breaks my heart".
"We do not have the luxury of pretending that all individuals coming to this country as a family unit are, in fact, a family", she said. None of those laws or precedents mean that children must be taken away from their parents.
The settlement says the government is required to release immigrant children from detention without unnecessary delay - generally within 20 days - to parents, relatives, or licensed programs.
The stories of babies ripped from the arms of their mothers, scenes of jail-like facilities, and reports of plans to house the growing number of children in tent cities have drawn an increasingly sharp public outcry over the last week.
President Donald Trump defended his controversial immigration policies on Monday ahead of a closely watched meeting with GOP lawmakers who have criticized his administration's "zero-tolerance" approach to border protection. "This is why we need more Republicans elected in November." - tweet Saturday. "I visited the detention centers myself".
Some of Trump's fellow Republicans have said the policy must end. "We will not apologize for the job we do".
The website also includes a PDF flyer titled Next Steps for Families which details how a parent can locate their detained child, but doesn't supply any instructions on how to be reunited with the child.
"That's a very cowardly response", Nielsen said.
Mr Trump has sought to use the widespread outrage over the family separations to push through other immigration priorities that have stalled in Congress, such as funding for his long-promised wall along the Mexican border.
Lawmakers have traveled to South Texas where hundreds of children separated from their parents are being held to speak out against the zero-tolerance policy.