Millie Bobby Brown was "scared" to go to school because of bullying.
The 15-year-old actress reflected on her ordeal and how "helpless" she felt in what was supposed to be a "safe place" as she gave a speech during the UN Summit To Demand Rights For Every Child On World Children's Day on Wednesday (20.11.19) in New York City.
She said: "I'm proud to add my voice to all those around the world who are asking for solutions to today's problems such as bullying, access to education, mental health awareness, suicide prevention and climate change.
"In world capitals, in buildings like this, adults talk about children's rights. But today, young people don't want to be talked about. They want to do the talking. In the words of one young person: "Be an active voice. Don't let things go unnoticed.
"So today, I want to talk about an issue that is very personal to me. Something that so often goes unnoticed - but causes real suffering. Bullying. Like David [Beckham], I've been very lucky in my life. I take nothing for granted. But I also know what it feels like to be vulnerable. At school, I was bullied by a group of students. I remember feeling helpless. School used to be a safe place. Now I was scared to go."
But the 'Stranger Things' star feels "lucky" that she had strong support around her and vowed to continue speaking out and advocating for those who are "struggling in the darkness".
She continued: "I was lucky. With the help of my friends, family and people around me, I was able to overcome these negative feelings and take my power back.
"But millions of children aren't so lucky. They're still struggling in the darkness. Wrestling with fear. With insecurity. Bullying and online threats are never harmless. Never just words. It puts children's mental health at risk. It causes stress.
"And in the most extreme cases, and in areas around the world where conflict and violence are daily threats, it can lead to self-harm. Sickness. And even suicide.
"In my role as Goodwill Ambassador, I will continue talking about this issue wherever I go. Every one of you here today can be the loudspeaker that turns our voices into real change. Into policies, programmes, laws and investments that keep children safe. That makes our world a better, healthier, stronger place for all."