Beat is a national eating disorder charity. Their website has information about eating disorders and difficulties, and the support available to people experiencing these problems. https://www.b-eat.co.uk/
Young Minds provide information about the mental health and wellbeing of children and young people, including information about eating disorders: http://www.youngminds.org.uk/
If you are concerned that you or someone you know might be affected by an eating disorder, talk to an adult you trust and arrange an appointment to see your GP.