New data shows thousands of young people are struggling with mental health problems in Surrey and North East Hampshire.
Mental health charities have warned about an underreported "national crisis" among children, and say short-staffed public services cannot tackle the problem unless funding is increased.
The rate is below areas such as County Durham, where more than 60 in every 1,000 children required mental health assistance.
A recent report by the Association of Child Psychotherapists said child and adolescent mental health services are facing a "serious and worsening crisis" due to underfunding.
Dr Nick Waggett, chief executive of the Association of Child Psychotherapists, said:
"These new figures confirm national prevalence data showing that mental illness amongst children and young people is increasing.
"It is important that the needs of the most unwell and vulnerable children are recognised and that investment is put into their care.
"At the same time, services must be expanded to meet the rise in mental health problems and address the long-standing shortfall in services for children, young people and their families."