The number of children diagnosed with mental illnesses has more than doubled in five years and cases of intentional self-harm have also surged.
Recently published figures show the figure of patients under 18 who went to A&E and were diagnosed with having a mental disorder has grown each year from just under 7,000 in 2010/11 to almost 15,000 in 2014/15.
The number of patients under 18 who have been identified in A&E as having intentionally self-harmed has also from from 13,504 in 2010/11 to 17,019 in 2014/15.
Cases where A&E patients under the age of 18 were diagnosed with psychiatric disorders and were identified as having intentionally self-harmed rose from 1,098 in 2010/11 to 2,313 in 2014/15.
Norman Lamb, the Liberal Democrat former health minister who asked the written parliamentary question which prompted the publication of the figures, said: "The Government is failing to support children and young people by not delivering the investment that was agreed before the general election.
"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."
He also said the statistics show 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".
He added: "I am calling on the Government to make up the shortfall immediately, and to deliver on its promise to provide the full £1.25bn over the next five years."