The number of children being admitted to A&E and diagnosed with psychiatric disorders - and had also intentionally harmed themselves - has more than doubled since 2011.
Recently published figures show that self-harm among those with mental health problems under the age of 18 rose from 1,098 in 2010/11 to 2,313 in 2014/15.
The figures also come as the number of children diagnosed with mental illnesses has more than doubled in five years, and cases of intentional self-harm have also surged.
Patients under 18 who went to A&E and were diagnosed with having a mental disorder has increased each year from just under 7,000 in 2010/11 to almost 15,000 in 2014/15.
And the number of young patients who have been identified in A&E as having intentionally self-harmed themselves has also increased from 13,504 in 2010/11 to 17,019 in 2014/15.
Norman Lamb, the Liberal Democrat MP and former health minister who asked the written parliamentary question which prompted the publication of the figures, said the government was "failing to support" children and young people by not delivering the investment that was agreed before the general election.
He told the Independent: "In March 2015, Nick Clegg and I announced £1.25 billion to be spent over five years on improving young people's mental health services, but the Government has already underspent by £107 million in the first year.
"This is unacceptable, and these latest figures show the need for urgent investment in preventative services and community care to stop young people from reaching crisis point."
Lamb said the statistics also showed there is an "absolute need to introduce the same right to get treatment on a timely basis for children and young people suffering mental ill health as others enjoy".
Lamb is calling on the Government to make-up the funding shortfall immediately, and to "deliver on its promise" to provide the full £1.25bn over the next five years.
The Centre for Mental Health, a leading charity, said on Wednesday that the rise of children and young people attending A&E as a result of self-harm injuries "is a cause for major concern".
A spokesman said: "We know that a large proportion of children who self-harm have underlying mental health difficulties and it is important that they are offered effective help for those problems as quickly as possible.
"Mental health problems are extremely common among children and young people, affecting about one in ten at any time. Three-quarters of them get no support at all and some end up in a crisis because of a lack of early help."
The spokesman said children needed earlier and better support "to prevent crises from happening" and the health service needed to ensure experts were available whenever required.