The Duchess of Cambridge has recorded a personal message to try and spur children on to be comfortable in their own skin.
Kate, who is pregnant with her third child, also says adults should help encourage children on to be the best versions of themselves.
In a specially-recorded video released to launch Children's Mental Health Week 2018 (February 5-11), she said: "Childhood is an incredibly important moment in our lives.
"It is the time when we explore our personalities, discover the potential that lies within us and learn how to be ourselves.
"Our experience of the world at this early stage helps to shape who we become as adults, how we begin to feel comfortable in our own skin."
Her words tie in with a new campaign by the children's mental health charity Place2Be - called Being Ourselves - which helps youngsters tackle low self-esteem and create a positive images of themselves. Some children compare themselves negatively to others, especially online, according to Place2Be.
Kate, who has been a Place2Be patron since 2013, filmed the video message during last month's visit to Reach Academy Feltham, west London. She spoke to pupils, parents and teachers about the impact of the scheme which tries to spot potential problems early and give support in familiar surroundings.
Low self-esteem affects more than eight in 10 of the pupils who get Place2Be's one-to-one help. The back-up given to help boost confidence can help the children to cope with life's challenges.
Kate said: "Some children will be facing tougher challenges than others, but I firmly believe that while we cannot change their circumstances, we can ensure that every child is given the best possible support to ensure they fulfil their true potential.
"This is best achieved when we, the adults in their lives, work together to give children the emotional strength they need to face their futures and thrive
"Whether we are school leaders, teachers, support staff or parents, we each have a role to play.
"When we are open and honest with each other about the challenges we face, we can work together to ensure the children in our care have the chance to become the best version of themselves."
Place2Be chief executive Catherine Roche said: "We know from our work in schools that some children find it difficult to think of themselves positively, as it's all too easy nowadays to compare ourselves negatively to others, especially online.
"This Children's Mental Health Week we are encouraging everyone, and especially children and young people, to focus on what makes them who they are, and to celebrate their unique qualities and strengths.
"We'll all face difficult times in our lives, but helping children to have a positive view of themselves can help them find the inner strength and resilience to cope with those challenges."
Ed Vainker, Principal at Reach Academy Feltham, added: "The week, and the interest and commitment of the Duchess offers an opportunity to celebrate the great work done by schools, parents and other groups around the country to support young people to become confident, resilient adults."