Almost a million children in Britain are affected by domestic violence, either as victims or witnesses, a new study says.
The number has increased more than 22 per cent over the past decade.
Some 52 per cent of parents with children under 18 experience frequent or serious conflict, according to YouGov in a poll for the charity 4Children.
Of those relatives who have regular clashes, 8 per cent – or 600,000 – are so violent that physical injuries occur.
The report is the first to expose the true scale of violence within families, as it examines not just abuse between couples, but also physical abuse of children by their parents, between siblings and attacks by children on their parents.
Despite the widespread problem, four out of five families affected do not get help for domestic violence.
Those who do seek help find it increasingly scarce: more than a quarter of all councils have cut back their funding for domestic abuse support over the past two years.
One of the least recorded crimes is attacks by teenagers on their parents.
The study was able to obtain statistics for it only from the Metropolitan Police, who responded to more than 1,900 incidents of over-18s attacking their own parents in London in 2009-10.
Anne Longfield OBE, chief executive of 4Children, said: "Domestic violence is familiar ground, but family violence is often hidden from view. Conflict need not turn to violence if families get the help they need. Violence in the family threatens lives, breaks up families and has severe ongoing psychological and physical effects on hundreds of thousands of parents and children every year.
"Family violence is one of the biggest causes of family crisis in the UK, one that puts lives at risk, isolates people, undermines good mental health and costs the taxpayer in excess of £3.1bn a year in costs to the NHS, the courts and social services."
The scale of abuse also has a significant impact on future generations. According to research from the US, children who have experienced violence in the home are up to 24 times more likely to commit sexual assault than those from non-violent homes. Victims of child abuse are a third more likely to harm their own children.
The neurological impact on children of domestic violence is similar to soldiers with post-traumatic stress disorder, according to the latest research. Dr Eamon McCrory, a developmental neuroscientist at UCL, said: "We knew that domestic violence can significantly increase the risk of later mental health problems, but I found that kids exposed to family violence showed higher neural activity to threats such as angry faces in the same regions that show heightened activity in soldiers exposed to combat."
Sarah, 31, whose name has been changed to protect her family, is from Colchester, Essex. She has three children and escaped from an abusive marriage two years ago.
"I was married to my husband for 10 years before I left. Every six months he'd blow up and there'd be a violent outburst. When I was seven months pregnant with my first child, he dragged me around by my hair and locked me in the bedroom. I never knew I had a problem till I read an article in the paper about domestic violence with a checklist. I ticked every category.
"When I asked if we could have a break he smashed a vase and a canvas on my head. I had to call the police several times. Eventually I escaped and went to a refuge. My eldest boy was quite violent when we first left. He was seven and he'd hit me and pulled a centimetre-wide chunk of my hair out. My youngest, who's four, has counselling. He's got the emotional age of an 18-month-old because of the trauma."
Mark Brooks, chair of the charity ManKind, which supports male victims of domestic abuse, said:
"Research like this shows domestic abuse is not one-dimensional but multi-dimensional, and this will go a long way to ensuring that all victims of domestic abuse are supported, regardless of gender, race or sexuality."