More than a quarter of children referred for mental health support in England last year - some of whom had even attempted suicide - were sent away without help, it has been reported.
A review of mental health services by the Children's Commissioner discovered 13% of youngsters with life-threatening conditions were not allowed specialist treatment, according to the BBC.
Even those with the most serious illnesses who secured treatment faced lengthy delays, with an average waiting time of 110 days, The Times newspaper said.
Anne Longfield accused Children and Adolescent Mental Health Services (CAMHS), the NHS body responsible for young people's mental health services, of "playing Russian roulette" with young lives, the newspaper reported.
Average waiting times ranged from 14 days in a trust in north-west England to 200 days at one in the West Midlands, while around 35% of trusts said they would restrict access to services for children who missed appointments, the review found, according to the Press Association.
Around 248,000 children were referred for specialist mental health treatment last year but 28% were refused, mostly on the grounds that their illness was not yet serious enough to merit specialist help, The Times reported.
Longfield said: "If a young person with a life-threatening mental health condition has to wait six months to see a specialist, we are playing Russian roulette with their lives. In many parts of the country young people's mental health support seems to be rationed.
"I've heard from far too many children who have been denied support or struck off the list because they missed appointments. I've heard from others whose GPs could not manage their condition and who had to wait months to see a specialist whilst struggling with their conditions,"
The commissioner obtained data from 48 of England's 60 child and adolescent mental health service trusts, according to the BBC.