In cities across the country yesterday, tens of thousands of people gatheredto draw attention to several high profile deaths of unarmed black men at the hands of police.People marched in New York, Los Angeles, Boston and Washington, D.C.Hands up, don't shoot. Hands up, don't shoot. Hands up, don't shoot.Here in Washington, protesters of all ages began their march at Freedom Plaza near the White House.NPR's Laura Sullivan followed demonstrators as the march got underway.I can't breathe. I can't breathe.Thousands of people have flooded onto Pennsylvania Avenue here in Washington, D.C.to march from the White House to the U.S. Capitol about a mile here up the road to protest what they believe is excessive police violence.There are hundreds of posters with the names of unarmed black men that have died in altercations with police.And even more posters that say black lives matter....No justice, no peace, don't trust the police. They shot Mike Brown in the middle of the street. No justice, no peace...This is a group of kids from Brooklyn, New York. They're from two high schools.Shenica Odom came down from New York with these 21 high schoolers.And they're ready. These chants that they're saying are chants that they came up in their group because it resonates with them.And it's not just rhetoric for them, this is the life that they live.This is the next generation of civil rights and social justice activists.For as many young marchers like these students as there were, there were just as many older marchers ― men and women, black and white.