The National Library of Medicine's MedlinePlus gathers links on this page about numerous health issues for children and teens including abuse, ADHD, alcohol, child development, nutrition, learning disorders, and many other health concerns.
The Centers for Disease Control and Prevention (CDC) provides webpages and factsheets for numerous children's and teen health concerns such as autism, body mass index, developmental disabilities and screening, asthma, immunizations, oral health, and sun safety.
Produced by the Nemours Center for Children's Health Media, this site aims to be "free of doctor speak," and provides information resources in separate pages for parents, children, and teens. As with the FamilyDoctor resource above, the children's page is accessible and friendly for children seeking information.
Produced by the Office on Women's Health of the U.S. Department of Health and Human Services, this site helps pre-teen and teen girls learn about health issues including body, fitness, nutrition, illness and disability, drugs, alcohol and smoking, feelings and relationships, bullying and safety, and environmental health.