Family disputes are a major cause of children's unhappiness, says research
Unhappiness in children is more likely to be influenced by conflict in their family than the family's structure, research suggests.
A study by the Children's Society says family arguments are more damaging for children than factors such as whether they live with married parents.
This survey of well-being was based on the views of 7,000 children in England aged between 10 and 15.
It found that about 7% of children were "significantly" unhappy.
Among a cohort of 1.8 million children - this would mean there are 140,000 deeply unhappy children in these age groups.
The charity wanted to investigate how children experienced unhappiness and happiness - asking them to record their feelings on a scale of 0 to 10.
It found that living in a happy household, where people got along together, was a major positive factor in children's sense of well-being.
But when children were in a home where people were fighting there was a sharply negative impact - calculated as representing 20% of the variation between happiness and unhappiness.
In contrast, the type of family structure - such as whether children were living in a single-parent family - had a more marginal impact, calculated as a 2% disadvantage for those not living with both parents.
But the experience of separation - and changes in the adults living with children - did reduce happiness, pushing down the sense of happiness to 6.8 out of 10, below the overall average of 7.7.
Children also reported that anxiety about their appearance made them unhappy.
In particular, girls were worried about how they looked - being twice as likely to be unhappy about their appearance than boys.
Overall, boys were found to be happier than girls.
Asked about their level of happiness, a large proportion of children were broadly positive - averaging 7.7 out of 10 - but more children reported feelings of unhappiness as they grew older and entered their teenage years.
Other factors identified as potentially causing unhappiness were the areas where the children lived and their schools.
The charity wants to use this large-scale study to create a benchmark for a "well-being index" - so that the impact of future changes in policy can be measured.
The research is published a week after both Labour and the Conservatives launched plans to support the family - with promises to back marriage and stable relationships.
And updated guidelines for sex education in schools in England, published on Monday, emphasised the importance of marriage and strong relationships.
"Family conflict emerges in this study as a major cause of childhood unhappiness, and so it is vital that families can get the sort of family mediation and counselling the Children's Society offers to help them resolve and avoid conflicts," said the Children's Society's chief executive, Bob Reitemeier.
"This report is a stark reminder that our actions as adults can have a profound impact on our children's well-being and the importance of listening to what children are telling us."
The study was produced with the University of York and the survey's co-author, Jonathan Bradshaw, said it "establishes a valuable benchmark that we can use to track changes in well-being over time".