Children make up a fifth of people receiving NHS help for mental health problems in Calderdale, figures reveal.
With the General Election looming, more than 140 children's organisations have called on political leaders to "put children at the heart of this election".
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Campaigners say social problems including mental health, youth violence and poverty risk leaving millions of youngsters "scarred for life".
New NHS Digital data shows 10,200 people – five per cent of Calderdale's population – were seen by mental health services in 2018-19.
Of these, 1,945 (19 per cent) were under 18.
This means four per cent of children in the area were in contact with mental health services, compared to the five per cent average across England.
The statistics, rounded to avoid identification, also show around five children ended up in hospital receiving treatment.
Across England, mental health services treated 630,000 children and young people over the year.
The Association of Child Psychotherapists warned child and adolescent mental health services face a "serious and worsening crisis" due to underfunding.
Organisations including Action for Children, Barnardo's, the NSPCC and The Children's Society say youngers are being "crowded out" of discussions on the nation's future, leaving their needs overlooked.
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Their open letter urges the party leaders to prioritise combatting problems children face when the next government takes office.
"There are almost 14 million children in the UK but their voices are missing from the national conversation and far too little attention has been paid to their needs, particularly those of the most vulnerable," it reads.
"Instead, the debate on Brexit means the issues affecting children are being crowded out of the national debate.
"We are asking each of you to put children at the heart of this election."
One in eight children and young people aged between five and 19 years old have at least one mental health condition, according to the charities.
Services which vulnerable children rely on are facing a funding crisis while demand continues to rise, they add.
The Children's Commissioner for England estimates it will cost £10 billion "to fix the safety net".
The investment would deal with issues including domestic abuse, youth violence, poor education and children's mental health.