Almost a quarter of a million children in the UK - the equivalent of 219,000 - are apparently "unhappy".
That's according to new figures from The Children's Society, which put together something called the Good Childhood Report every year.
It says that children's happiness with life is at its lowest since 2009.
The report says that the reasons why many children aren't happy relate to things like appearance, friendships and school.
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The Good Childhood Report says that nearly one in 12 boys (7.7%) aged 10 to 15 years old - the equivalent of 180,000 - are unhappy with their appearance.
Although boys remain consistently happier with their appearance than girls, the gap has narrowed and boys' happiness with their appearance was significantly lower in 2016-17 than it was in 2009-10.
Over-13s were significantly less happy with how they look compared to 10 to 12 year olds.
Read more about how body image pressure for boys is affecting their mental health.
One in eight children (11.8%) are also unhappy with school. In fact, the children are more unhappy about school now than at any time in the past ten years.
More than a third (33%) of 10 to 17 year olds voiced concerns about whether or not they will have enough money in the future, with more than a quarter (29%) worrying about having a job.
Children's happiness with their friendships is also decreasing, with 2.8% of children feeling unhappy with their friends.
The wider research suggests that this could be down to a wide range of factors.
These included bullying, not being unable to spend time with friends outside of school, spending too much time on social media and loneliness.
About one in five worried about the economy and Brexit.
The Children's Society boss Mark Russell says: "Many young people tell us they feel side-lined and ignored by those in power.
The Children's Society is committed to listening to young people, and working with them to speak up and speak out, to enable every child to thrive - not just survive."
The charity also wants the government to do more to check up on how happy children aged 11 to 18 are, by making checks at schools and colleges.
They hope this would help to improve the experiences of young people and ensure that issues can be recorded and acted upon for future generations.
If you are worried about or affected by the issues in this article, there is lots of support out there for you.
Speak to an adult you trust, like a parent, guardian or a teacher.
You can also contact Childline - a counselling charity for people aged 18 and under - on 0800 1111 for free at any time.