The ceremony was among numerous events this year taking stock of progress achieved under the landmark Convention on the Rights of the Child.
"In world capitals and buildings like this, adults talk about children's rights. But today, young people don't want to be talked about. We want to do the talking", declared actress Millie Bobby Brown, star of the hit series 'Stranger Things' and the youngest-ever Goodwill Ambassador with the UN Children's Fund (UNICEF),
Indeed, they have a lot to say.
Dante Vegara, an 11-year-old climate activist from Chile, had one request for the international community: Act now to protect our planet.
"Very often, issues of the environment and climate change are postponed because there are more urgent things to resolve and I am concerned many adults continue to see things that way," he said.
"Climate change is a very severe problem. Girls and boys have something to say because we are the ones who will inherit a sicker and sicker world. Without a healthy environment, all our rights are threatened."
Though no longer a child, football legend David Beckham recalled his youth in the East End of London, where family, teachers and later, coaches, supported his dream of becoming a soccer player.
As a UNICEF Goodwill Ambassador since 2005, Mr. Beckham has seen how scores of children worldwide have not been as fortunate.
"Children hungry and sick. Children living through wars. Children who lost their parents in earthquakes and floods. Girls and boys with different stories and backgrounds from my own, but like all children they have one thing in common: they have ambitions and they have dreams for a better future," he said.
The anniversary of the child rights convention provides an opportunity for adults and children to work together to build that brighter future, UN Deputy Secretary-General Amina Mohammed told the gathering.
Although important markers have been achieved since its adoption, including the fact that more children are now in school, millions of the world's poorest children are still being left behind.
They include children still living in slums, or who go to bed hungry, or who have no access to health care and education. Children also have been forced to fight in wars, labelled as terrorists, suffered sexual abuse or trafficked into bondage, among untold other horrors.
And while three decades of technological developments have empowered children, UN human rights high commissioner Michelle Bachelet reported how the Internet has been used to bully, intimidate and exploit children.
Ms. Brown, the UNICEF Goodwill Ambassador, revealed that she too has been victimized.
"Like millions of other girls around the world, I've also been bullied and harassed online," she said. "It's a terrifying feeling to look at your phone and see that the messages that people are sending you are filled with anger, hate and even threats."
The President of the General Assembly, which brings together all 193 UN Member States, underlined the need to make girls a priority. Some 650 million girls globally reportedly have been married off before turning 18.
"It is crucial that girls are encouraged to stay in school and attain necessary capacity for mental and human capacity development," Tijjani Muhammad-Bande said in his opening address.
Tackling climate change, ending poverty and hunger, providing quality education, and empowering women and girls are among the objectives of the Sustainable Development Goals, which have a deadline of 2030.
As Ms. Mohammed, the UN deputy chief, pointed out, there is still more work ahead and children must be at the heart of all efforts.
"The most important leaders of our time are children. Passionate, engaged child activists from all regions of the world are sending a wakeup call to older generations. They are rightly demanding action on the climate crisis, on gender inequality, on human rights and on economic systems that prioritize short-term gains over the health of our planet and its people," she said.
"Thirty years after the Convention on the Rights of the Child, it is time to listen to the voices of our children and hear their pleas for the broken promises to be fulfilled."