Over 9,000 referrals were made to the trust between 2015 and 2017.
Over 500 children referred to Humber NHS mental health services have been rejected for treatment in the last two years.
The NSPCC's obtained new figures via a Freedom of Information request to NHS Trusts in England which found the equivalent of 150 children a day were rejected for treatment between 2015 and 2017.
From a total of 652,023 cases referred to child and adolescent mental health services (CAMHS), 109,613 children were turned away.
But the charity fears the number of young people being dismissed from mental health services could be significantly higher, as one in five of the Trusts which responded to the request failed to disclose the number of rejected referrals.
The NSPCC is now calling on the Government to shift the focus of child mental health services towards early intervention.
Early intervention is key to minimising the long-term impact of mental health. Research shows that half of mental health conditions experienced by adults first develop before the age of 15, with three in four cases present by the age of 183.
A spokesperson for Humber NHS Foundation Trust says: “We are committed to giving the best care to all children and young people who are referred to our child and adolescent mental health service (CAMHS).
"However, there may be times when some referrals are rejected, and this could be for a number of reasons. For example, there may be duplicate referrals for the same young person, so one or more of these will be rejected; the application may be inappropriate for reasons such as the young person is living in an area in which we do not offer a service. Lastly, the referral may be incomplete, therefore we would need to wait while further information is acquired.
"The CAMHS service is also part of the wider community of support in which young people’s mental health is supported by a number of organisations. Local CAMHS services have worked with this wider community of support to transform local services to ensure that the young people of Hull and East Riding get the right level of support offered by the most appropriate service.
"This will mean that sometimes CAMHS is not the best service to offer that support. It will be on these occasions that the CAMHS service will work with the referrer to identify the most appropriate support.
"Access to the Trust’s CAMHS service is through our Contact Points for Hull and East Riding. Our highly skilled clinicians provide support for early intervention and prevention by using assessment, consultation and psycho-education, working with young people, their family/carers and other professionals. This means that in many cases children and young people do not have to come through to a specialist service."