The increase is blamed on lockdowns, social media and a lack of adequate mental health care by experts.
In one case, a child waited more than four years to get professional NHS support.
The biggest rise in hospital admissions for self-harm and self-poisoning was among girls ages just nine to 12.
A total of 875 among that group needed in-patient treatment from April 2020 to April 2021.
That leapt to 1,450 the following year – a spike of 65 per cent.
Admissions grew by 23 per cent in girls aged 13 to 17 in the same period to last April.
There were 20,783 incidents involving them, against 16,867 a year earlier.
Boys have not escaped the record rates, with 175 boys aged nine to 12 taken in by hospitals in the year to last April.
That’s up nine percent on the 161 cases 12 months before. Hospitals admitted 2,911 boys aged 13 to 17 between April 2021 to April 2022, a three per cent climb on the 2,833 in the previous 12 months.
The data from NHS Digital reveals how cases involving girls have snowballed over 10 years.
A decade ago hospitals admitted 307 girls aged nine to 12 – incidents are now 372 percent higher.
At the same time, figures show vulnerable children can wait months or years for help for mental health conditions on the NHS. One youngster missed out for at least 1,512 days – more than four years – in the Norfolk & Waveney Integrated Care Board (ICB) area.
Another had waited at least 1,113 days in Hampshire and the Isle of Wight. Eight of 29 Clinical Commissioning Groups and ICBs that responded to a Lib Dem Freedom of Information request admitted their average waits for mental health services topped 100 days.
Munira Wilson, the Lib Dem’s education spokeswoman, branded the situation “disgraceful”, adding that children in dire need of help had been left to suffer. Rosamund McNeil, of the National Education Union, believes the pandemic increased mental health difficulties among youngsters.
She said worst hit were “children in poverty, black children and those with pre-existing mental health conditions” – and she believes it will fuel self-harm rates further.
Mind’s Gemma Byrne demanded bold political leadership “including adequate funding for mental health services and a long-term, cross-government vision for mental health”.
