The single best go-to site on the internet will always be the Royal College of Psychiatrists. We have a very strong public engagement and engagement track record. See in particular the huge range of information leaflets on a range of conditions: https://www.rcpsych.ac.uk/
A superb series of E-Learning Resources for professionals training in childrens’ mental health, supported by Health Education England: https://www.minded.org.uk/
ACAMH – An academic organisation, designed for sharing best evidence and improving practice in Child and Adolescent Mental Health https://www.acamh.org/
In 2017, The Department of Health produced a Green Paper entitled: Transforming Children and Young People’s Mental Health Provision which can be dowloaded here: