The number of children calling ChildLine to confide in a counsellor about their parents' drinking and drug abuse has doubled in the past year, the charity has revealed.
The 24-hour helpline received 5,323 calls - more than 100 a week - from children scared by their parents' behaviour, a staggering rise on the 2,509 calls it fielded the year before.
Most of the children turning to the NSPCC-run service were between the ages of 12 and 15, but a substantial minority - one in 10 - were aged 11 or under and still at primary school.
In a stark warning, the charity said thousands of children live in fear of being on the receiving end of their parents' anger, with one in six saying they had fallen victim to physical violence by their mum or dad when they were under the influence.
Many children are being forced to live in dirty and even dangerous surroundings and lack many essentials including having enough to eat and clean clothes to wear because the household money is frittered away on booze, the charity warned.
The emotional trauma of their parents' substance abuse combined with their chaotic home lives is driving many children to depression, self harm and even suicidal thoughts, the NSPCC said.
One child, who cannot be identified, told ChildLine: "My dad has been drinking and taking drugs a lot recently - it's ruining our family.
"He gets angry when he has been drinking so he says nasty things to us like we are stupid and worthless. I'm finding it difficult to deal with because underneath it all I know he's a really good dad."
Tom Rahilly, head of services for families affected by alcohol and drugs at the NSPCC, said: "What we hear from children is that they are concerned that their parents are using drugs or alcohol to blot out worries in their lives around jobs, money and housing issues.
"The recent benefit cuts are hitting families in particular households. But the higher counselling rates could also be that more children are aware of ChildLine and that they have someone to turn to."
However, he warned against stereotyping and said that children from all walks of life, including middle class families, were affected by the problem.
He said that many children were faced with a "feeling of helplessness", while others were faced with the traumatic role reversal of playing parent to their own mother and father.
He said: "Many young people whose parents misuse drugs or alcohol end up being young carers themselves. That could mean caring for their mum or dad, or caring for their brothers or sisters.
"It has such a traumatic impact on the lives of those children. It is associated with missing school and not being able to excel because they are busy being carers."
The charity warned the figures were just the tip of the iceberg, and estimates that some 250,000 children in the UK have parents with drug problems, and three in 10 children live with at least one binge-drinking parent.
The numbers contrast with a long-term fall in violent crime in England and Wales, thought to be partially influenced by the rising cost of alcohol.
Sue Minto, head of ChildLine, said: "It's heart-breaking that so many young people struggle alone because they do not know where to go for help or are unsure of what might happen if they speak to someone. They may fear being taken away from their families by social services and put into care and believe that they are protecting their family by keeping quiet.
"Some children tell us their parents are under stress and it may be that they are using drink and drugs to blot out worries about jobs, money or housing issues. But whatever the reasons behind the rise, it's vital that anyone who knows a parent with drink or drug problems takes action to get that family help so that their children are protected."
Children can seek help by contacting ChildLine on 0800 1111 or at childline.org.uk. Adults with concerns about a child should call the NSPCC helpline on 0808 800 5000.