Self-esteem is how you think about yourself and the beliefs you have about yourself. These might be beliefs about how you look, your personality, your work, your future or how you get on with people.
If you have healthy self-esteem you will generally think positively about yourself, notice things you do well and feel good about yourself. You will still experience difficult times in life, and have worries, but you will be more confident and able to deal with these.
If you have low self-esteem you might generally think negatively about yourself and focus on weaknesses or mistakes you have made, you might find it hard to see the good parts about yourself that other people see.
It can be difficult to understand why someone has low self-esteem - you might see them as confident, outgoing, kind, chatty, pretty, interesting, funny, honest - but it can be hard to see yourself how other people see you. If you have low self-esteem it can seem impossible to believe anything positive about yourself - even if somebody else points it out. This video "You're more beautiful than you think" shows how sometimes what you see can be very different from what someone else sees.
There are a few things you can do to try and build up your self-esteem - you can read more about this on the Mind page.
The Dove Self-Esteem Project was started to help girls and young women improve their self-esteem and body confidence. They have lots of articles and advice for parents of girls and young women - it could be a good way to start a conversation about self-esteem, or discuss anything you or your daughter may be worried about. There is no information specially for boys - but a lot of the advice could apply to both boys and girls.