They were processed and being released, according to Capitol Police, a D.C. agency.
It began at Freedom Plaza, then the group marched to the Department of Justice, where police had surrounded the building in preparation for the protest.
More than 2,000 children who arrived illegally in the United States with adult relatives were separated from them and placed in detention facilities or with foster families around the United States.
A Democratic congresswoman was among about 575 people arrested at a rally protesting the Trump administration's zero-tolerance policy on immigration.
Amnesty International USA, the Anti-Defamation League, the Southern Poverty Law Center and the Women's March are among them.
"When we were advocating to keep families together and end family separations, we were not advocating for family incarceration", said Linda Sarsour, one of the leaders of the Women's March.
Hundreds of activists protest the Trump administration's approach to illegal border crossings and separation of children from immigrant parents, in the Hart Senate Office Building on Capitol Hill in Washington, Thursday, June 28, 2018. "Camps for children is just as wrong as camps for children and adults".
"I have two kids, and as a white mother, there is nearly no circumstance that they would be taken away from me - ever", said Victoria Farris, who slept Wednesday night in All Souls Church after participating in civil disobedience training.
"This is a moment of outrage and we need people in the streets", she said.
The Washington, D.C., protest, which will take place in Lafayette Square near the White House, is slated to feature several speakers, including Hamilton creator Lin-Manuel Miranda. "It is inhumane how these children have been treated, and the president's executive order did nothing to address it", Stephanie Hunnell and Sylvia Breitowich, organizers of a rally in Asbury Park, said in a statement.