"This has to stop."
Tolley said advice from the State Services Commission, Treasury and Ministry for Social Development had recommended a stand-alone department be established, given the scale of the proposed reforms.
CYF is currently a service of the Ministry of Social Development.
The new ministry will have a much wider brief than the existing CYF, with a $1.3 billion annual budget by 2019-20 to buy extra education, health, employment and social services for the families of all "vulnerable" children.
Numbers are uncertain, but an expert panel led by Dame Paula Rebstock says one in five children are known to CYF by age 17.
Using that benchmark, it was estimated there are about 230,000 children and young people currently under age 18 who might experience vulnerability at some point in their childhood.
We know that a child that grows up in deprivation and poverty also has poor outcomes. We should be focussed on lifting the wellbeing of all children.
Tolley said the new ministry would focus on five core services - prevention, intensive intervention, care support services, transition support and a youth justice service.
Related legislation currently before Parliament will raise the age of state care and protection to 18, and establish an independent youth advocacy service.
The new ministry will be reviewed after two years.
Labour's spokeswoman for children Jacinda Ardern told the Herald that the name was disappointing as it showed the ministry's scope would be too narrow.
"It suggests to me that they are going to take quite a narrow focus. I asked yesterday [during Parliament's question time] if the ministry would focus on child poverty issues as well and the minister refused to answer.
"We know that a child that grows up in deprivation and poverty also has poor outcomes. We should be focussed on lifting the wellbeing of all children."
Labour would establish a Ministry for Children governed by a board that includes public sector chief executives who work on issues that affect children, and then set targets for each ministry.
State Services Commissioner Peter Hughes today announced that Grainne Moss would be the chief executive of the Ministry for Vulnerable Children.
Moss was managing director at Bupa Care Services NZ, a private provider of health services to the elderly.