Here are some resources that you may find helpful:

Safer Internet // Advice for Parents

Internet Matters // Tips for Keeping Your Child Safe Online

NSPCC // Advice for Parents

CEOP // Advice regarding Age Appropriate Topics and Looking for Signs of Exploitation

https://www.nspcc.org.uk/keeping-children-safe/childrens-mental-health/

https://giveusashout.org/latest/self-harm-advice-parents-and-carers/

https://www.nhs.uk/mental-health/feelings-symptoms-behaviours/behaviours/eating-disorders/advice-for-parents/

https://www.youngminds.org.uk/parent/parents-a-z-mental-health-guide/eating-disorders/