Video report by David Hirst
Claire Throssell's ex-husband murdered their two children in a fire he started and she has championed the domestic abuse bill which will recognise children as victims of domestic abuse and ensure that provisions are in place for their safety.
The law will also define domestic abuse and provide shelter for victims when they need it.
Claire told ITV News: "This law will make things better for children and give them back their childhood and give any victim of domestic abuse, the support, love and protection that they need.
"They deserve better and from today the new domestic abuse bill is the first step forward in making sure that happens."
She added: "Hopefully this is a step forward and we're now telling perpetrators that they can't intimidate and frighten people and women and children, and men, who access this support will be safe."
The government says it has set £300 million aside to tackle domestic abuse, but campaigners have said it doesn't go far enough.
Claire says that she will continue to campaign for even greater protection for children caught up in domestic violence.
She wants the government to overhaul custody laws - her two son's Jack and Paul were allowed to see their father unsupervised against her wishes.
She said that today's law felt like the halfway point to making sure that children are safe.
The Chief Executive of the children's charity Barnardo’s Javed Khan said: “It has been a long time coming but I’m very pleased the Domestic Abuse Bill has finally become law today, four years after it was announced in the Queen’s Speech.
"Living in a home with domestic abuse can have a devastating impact on children's well being, education and future relationships, and the trauma often follows them into adulthood.
"For years children have been labelled as ‘witnesses’ or ‘bystanders’, but from today the law will recognise that children are direct victims of domestic abuse.
"And children who have been uprooted from their home and moved into a refuge for their own safety should be able to access the support they need to recover."
Where to seek help if you and your children are victims of domestic abuse:
Call the National Domestic Abuse Helpline for free and confidential advice, 24 hours a day on 0808 2000 247.
Women's Aid has a range of direct services for survivors, including a live chat service and an online Survivors’ Forum.
The Men’s Advice Line is a confidential helpline for male victims of domestic abuse and those supporting them. Contact on: 0808 801 0327.
Chayn provides online help and resources in a number of languages about identifying manipulative situations and how friends can support those being abused.
If you are in an emergency situation and believe to be in immediate danger the advice is to call 999.