An abusive partner tried to strangle his girlfriend and stepdaughter and planned to lay in wait to kill his stepson.
Rory, the stepson, said it was the culmination of a decade of abuse that saw him try to kill himself after hearing his mum being raped.
In the year 2017-18, 1,065 under-16s were supported in refuges in Wales while 332 received counselling from Childline on domestic abuse.
Charities want to see more help.
NSPCC Cymru, Welsh Women's Aid and Children in Wales want specialist services in every region, local domestic violence strategies and healthy relationship education in school curriculums.
Rory, from Cardiff, now 20, said: "All I could see was this police van and I thought 'my mum's dead'.
"I kind of ran in and there were these two paramedics sat next to my mum. My mum had this huge handprint over her neck.
"And I could remember her saying 'ah it's OK, it's OK, it's over now'."
The attack happened after Rory's mother told her partner she was leaving him.
Thankfully his aunt walked in as it was happening and called the police.
Rory had spent his early years living with his grandparents but, when he was five, he moved in with his mother and her new partner.
Initially having a father figure excited him but, after a few weeks, he described him changing to "very grumpy, very angry all the time".
At first, there would be loud bangs as objects were thrown, but the abuse became more serious.
"I started realising that he was raping her most of the nights and I could hear her crying for help," Rory said.
"At one point I was screaming at him to get off of my mum, he slammed me into the wall and basically just held me there, laughing, neck first up off of the ground."
He described his stepdad as a builder - "a very big, strong guy" - who liked making his mum watch as he hit him.
On one occasion, Rory was beaten so badly he had to stay off school for a week.
"It was around about this time I started to feel trapped and as if I couldn't escape and I tried to commit suicide," he said.
"You know, watching some films I could see people would jump out of buildings and they would die."
But by jumping from his bedroom window, he only succeeded in breaking his leg.
After finding him, his stepdad left him to "sleep it off" in the garden overnight.
Even though he was petrified of him, he said teachers and friends thought he was a great dad - meaning he got away with abuse for nine years until Rory was 15.
His stepdad was taken to court where he was given 100 hours of community service.
"For somebody to take nine years away from both me and my mum and to only have 100 hours of his life taken away," Rory said.
"I felt like that was so pathetic of a sentence that I just walked around with an anger and hatred for everyone.
"I ended up getting diagnosed with severe depression and tried to commit suicide [for a second time]."
With support he is coming to terms with the abuse, and the three charities have called for more help for young people growing up in violent circumstances.
NSPCC Cymru's Vivienne Laing said it can cause "long-term problems into adulthood".
"It is vital that children and young people learn about healthy relationships in schools and know who to turn to for help," she said.
Welsh Women's Aid's Gwendolyn Sterk said children "do not just witness domestic abuse, they experience it".
She called for better services to help across Wales.
South Wales Central AM David Melding, who chairs the children and young people's cross-party group in the Senedd, said: "We owe Rory so much for speaking out with such clarity.
"His words will bring new energy to the campaign in Wales to better protect children from the impact of parental domestic abuse and the need to provide services to help these child victims recover from their experiences."