The government is to invest £143m improving children's mental health services in England this year.
The funding is part of a £1.25bn package of increased spending on children and adolescents' mental health services announced in March's budget.
The money for 2015/16 is short of the £250m Department of Health officials had expected to be spent this year.
A further £30m will be spent helping people with eating disorders this year, the department said.
The details are likely to include a guarantee that by 2020, 95% of patients will be seen within four weeks of being referred, with the most urgent cases seen within a week.
On mental health spending, a department spokeswoman said they had reduced this year's spending to ensure the money was properly invested.
She added they were fully committed to spending the whole £1.25bn over the course of the Parliament.
Children's mental health services in England are under severe strain, with long waiting times for treatment and few hospital beds, forcing some children to travel large distances for treatment.
Sarah Brennan, head of the charity Young Minds, said: "I'm not worried about how much they are spending this year as long as it's spent well, that the money is spent intelligently.
"They should use it to gear up this year, organise themselves and hire the right staff, allowing them to make next year a year of real transformation."
'Treat patients early'
Liberal Democrat MP Norman Lamb, the former care minister, said the shortfall in 2015/16 should be spent next year.
He added: "We also have to ensure that the government don't cut the money they give other areas of mental health funding, such as local authorities, who fund many psychiatric services for young people."
Dr Martin McShane, national clinical director for long-term conditions at NHS England, said: "The number of children and young people with an eating disorder is on the rise and it is right that the government has made this a priority and that we now have a clear waiting time standard.
"It is clinically proven that patients recover most quickly when we treat them as early and as close to home as possible.
"By prioritising our focus on doing this we can minimise the number of young people who end up needing more specialised in-patient care."