Nearby, a young girl stood beside her pregnant mother and held an unadorned cardboard sign that simply asked, “Am I next?”

Linda Wang, 39, said she was convinced there would be gun reform after the 2012 shooting at Sandy Hook Elementary School in Newtown, Conn., and was disappointed nothing happened. Originally from Taiwan, Ms. Wang said people outside the United States think gun violence in the country is “ridiculous.”

“There are shootings every day here,” said Ms. Wang, who has lived in the United States for 15 years. “We have to do something in America. This is not right.”

Omi Ford, 19, said she believed the large crowds emphasized how much energy is behind the gun control push this time around.

“I’m here to show that the Parkland students are not alone in this, in their thinking about this, even though some people act like they are,” said Ms. Ford, an acting student at the American Musical and Dramatic Academy in Los Angeles.