Lin-Manuel Miranda performed an a cappella rendition of “Dear Theodosia,” from his hit Broadway musical Hamilton on Saturday during a protest in Washington, D.C., against President Donald Trump’s now-halted family separation policy.

“Hamilton” creator Lin-Manuel Miranda dedicates lullaby to separated immigrant families: “We’re here because there’s parents right now who can’t sing lullabies to their kids” https://t.co/G40EcCxo0G pic.twitter.com/BqxPfHlow8 — CNN Politics (@CNNPolitics) June 30, 2018

“We’re here because there’s parents right now who can’t sing lullabies to their kids,” Miranda told attendees. “And, well, I’m just going to sing a lullaby that I wrote and this is for those parents. And we’re not going to stop until they can sing them to their kids again.”

LIVE: Lin-Manuel Miranda joins rally in Washington D.C. protesting family separation https://t.co/lQoGAy3i26 — NBC News (@NBCNews) June 30, 2018

Grammy award-winning singer Alicia Keys and actress America Ferrera joined Lin-Manuel Miranda at the march in the nation’s capital. In her remarks to attendees, Keys bizarrely claimed that President Trump could begin separating American families.

"If it can happen to any child, it can happen to my child, and your child, and all of our children," says singer Alicia Keys at the immigration rally in Washington, D.C. She then reads a letter written by a mother who was separated from her son. https://t.co/j5AGXVIZ6v pic.twitter.com/ZtGYN80Jy5 — CNN (@CNN) June 30, 2018

“I couldn’t imagine being separated from him … or scared about how he is being treated. So, this is all of our fight, because if it can happen to any child, it can happen to my child and your child and all of our children,” she said.

In Washington, D.C., an estimated 30,000 marchers gathered in Lafayette Park across from the White House in what was expected to be the largest protest of the day, stretching for hours under a searing sun. Firefighters at one point misted the crowd to help people cool off.

HAPPENING NOW: tens of thousands gather in Washington, DC to march in the Families Belong Together protest. #familiesbelongtogether #FamiliesBelongTogetherDC pic.twitter.com/E8oFSbUReM — CWS (@CWS_global) June 30, 2018

Protest in front of Trump International Hotel in Washington DC #FamiliesBelongTogetherMarch pic.twitter.com/89RUzPKLOs — franklin Brown (@franklin19788) June 30, 2018

“It’s upsetting. Families being separated, children in cages,” said Emilia Ramos, a cleaner in the district, fighting tears at the rally. “Seeing everyone together for this cause, it’s emotional.”

Around her, thousands waved signs: “I care,” some read, referencing a jacket that first lady Melania Trump wore when traveling to visit child migrants. The back of her jacket said, “I really don’t care, do U?” and it became a rallying cry for protesters Saturday.

Saturday’s demonstration comes after 575 people, along with a Democratic Congresswoman, were arrested Thursday at a rally protesting the Trump administration’s zero-tolerance policy on immigration.

NEW: Nearly 600 people arrested from Women's March protest in Hart Senate Office Building, Capitol Police says. https://t.co/kf0hY7iB12 pic.twitter.com/rjKVjeClGF — ABC News (@ABC) June 28, 2018

Rep. Pramila Jayapal (D-WA) told her nearly 60,000 followers that she was proud of her arrest and vowed to continue protesting the administration’s immigration policies.

“I was just arrested with 500+ women and @WomensMarch to say @RealDonaldTrump’s cruel zero-tolerance policy will not continue,” Jayapal tweeted.

I was just arrested with 500+ women and @WomensMarch to say @RealDonaldTrump’s cruel zero-tolerance policy will not continue. Not in our country. Not in our name.

June 30 we’re putting ourselves in the street again. Join us. https://t.co/DdRHeFtTTr pic.twitter.com/P9uK0Z1Zay — Rep. Pramila Jayapal (@RepJayapal) June 28, 2018

“Not in our country. Not in our name. June 30 we’re putting ourselves in the street again,” added the Democrat lawmaker.

Jayapal says she and other protesters were “here to fight for our families to be free, to fight for the ability of our kids to be with their parents — not in cages, not in prison, but able to live their lives free, safe and secure.” The Washington State Democrat and others were charged with unlawful demonstration for obstructing others in a public place.

Female protestors are gathered in the Senate Hart building on Capitol Hill. They’re shouting “abolish ICE!” to protest the Trump administration’s zero tolerance policy on immigration.@SenDuckworth just joined with her baby. pic.twitter.com/rWwQmznExL — Daniella Diaz (@DaniellaMicaela) June 28, 2018

Demonstrators, joined by some Democratic lawmakers, crowded the central lobby of the Hart Senate Office Building to protest Pres. Trump's immigration polices. Nearly 600 were charged by Capitol Police. https://t.co/OQO301FUSj pic.twitter.com/5VKRDnEyKG — ABC News (@ABC) June 28, 2018

Hundreds of demonstrators showed up at the Hart Senate Office Building to protest the Trump administration’s now-rescinded policy of separating migrant families at the southern border. Many protesters in the atrium of the Hart Senate building wore foil blankets similar to those given to migrants housed at U.S. detention facilities.

The Associated Press contributed to his report.