A stoic Thunberg calmly, but clearly, delivered her message to the room: "I'm doing this because world leaders are failing to protect the rights of the child by continuing to ignore the climate and ecological crisis."
Those words came just a short time after Thunberg delivered a powerful rebuke to world leaders at the U.N. Climate Action Summit.
"This is all wrong. I shouldn't be up here. I should be back in school on the other side of the ocean. ... You have stolen my dreams and my childhood with your empty words," Thunberg said.
The group of young people delivered a formal complaint Monday morning to the U.N. Committee on Rights of the Child, which alleges five of the world’s major economies have violated the human rights of children under the Convention on the Rights of the Child, the most ratified human rights treaty in the world.
Alexandria Villasenor, 14, of New York, addressed the room, saying, "Each one of us had our rights violated and denied -- we’re here, each one of us, to tell you how and why."
The kids, from a diverse set of countries spanning six continents, went on to say action and inaction by governments across the world have caused immediate harm and put lives at risk.
Like the other kids on stage, climate change is not an abstract problem for Villasenor, it’s personal.
The high schooler was in California visiting family last fall when the deadly Paradise fire broke out. The smoke was so bad it flared up her asthma and she had to be sent home.
She says Thunberg inspired her to take action.
"What really concerns me about the effects of the climate crisis in my future is that it will disrupt every aspect of young people's lives. It will choose where we choose to live, it will choose if you have a family, it will choose what we do for a career," Villasenor told ABC News.
The children want all countries to immediately adjust their climate goals and work together to confront what they call a crisis.
Carl Smith, 17, is a member of the indigenous Yupiaq tribe in Alaska.
His people have lived off the land for generations.
Climate change is incredibly real for them in Akiak, Alaska.
"It got so hot this summer that fish started floating in the river, dead," Smith told ABC News.
He said the rising temperatures and changing planet is difficult to deal with: "It is hard to see because it's the way I live, it's my culture and I don't want to see it die in my lifetime."
Villasenor delivered a message far beyond her years, "Living a normal life will just be us trying to survive, and surviving will be the new normal in the future."