Transcript for 'Welcome to the revolution': Students across the country rally for gun control reform

But the heart of the protest was right here in Washington where up to half a million people came from all over the country filling Pennsylvania avenue from the white house to the capitol. Welcome to the revolution. Reporter: Calls to action. We're done hiding. We're done being afraid. It is time to fight for our lives. Reporter: Punctuated by powerful moments. Since the time that I came out here, it has been 6 minutes and 20 seconds. The shooter had ceased shooting and will soon abandon his rifle. Fight for your lives before it's someone else's job. Reporter: Moments of silence and song. ??? with a corps husband of outrage. ??? Let's all reach out and touch ??? Reporter: We are the newseum. This crowd is loud and passionate and Pennsylvania avenue is packed. Families, generations brought together by that horrific school shooting. Oh, my god. Reporter: But the goals here are now much broader. Every day I worry AUT my 4-year-old going to school because of there being a potential incident at her school with a gun. Last week she had to do a lockdown drill. I am a gun owner myself. I probably own a dozen guns, I do not think you need assault -- citizens do not need an assault rifle. How old? Only 13. He was my only brother. Reporter: Christine can marching for her brother, pictured on her t-shirt who was a victim of gun violence. My family is marching in Tennessee and Massachusetts and Wisconsin and New York and Miami, so we're all walking together even though we're not together here. Reporter: This was personal and this was political. 15 years ago I lost my uncle Patrick to gun violence in Brooklyn, New York. My mother almost lost her daughter to the same gun violence in parkland, Florida. We've been fighting for this way too long and nothing has changed. And we need change now. Inaction is no longer safe and to that we say no more. Reporter: David hogg is one of a group of leaders who in just 37 days transformed his school from an object of pity into a symbol of passionate activism. We talked to David and his family days after the shooting. It was the first time his sister, 14-year-old Lauren, who lost four of her best friends had spoken about it. I saw my friends' faces on the news and I saw their names being called out and I just -- I collapsed. I couldn't handle it. Reporter: The entire family showed up for this weekend's March. When you looked out there today, what did you think? It was just profoundly moving and with all my friends that passed that day, I saw them in every single person that was here today. Just their joy, their happiness, their willingness to get stuff done, I always knew my friends were going to change this world but just unfortunate it was in this way. For you, Rebecca, what do you say to people who say, look, you know, in a month we'll all forget it. I say do you want it to be your child? And not just these children of privilege but think about the children in the inner cities, in Chicago, in New York and los Angeles, think about those children, you know. They're dealing with this every single day. Reporter: Their battle plan, register. Vote. Break the power of the NRA. Starting with the 2018 midterm elections. How many times have you been asked but change didn't happen after other shootings. Too many. Because change didn't really happen after those shootings but I don't like to say that because it's coming. It's still coming and it will come. But not if people don't get out and vote. That's what we're really trying to push here. This is just the beginning.

This transcript has been automatically generated and may not be 100% accurate.