Patient.co.uk is a very useful NHS information leaflet source.  It has a wide ranging base of information leaflets which you can search.

https://patient.info/

Arthritis UK has a very useful website with lots of information leaflets on common musculoskeletal conditions, medicines, alternative treatments, lifestyle and surgery.  Scroll to the bottom of the linked page.

https://www.arthritisresearchuk.org/information-and-support.aspx

Diet fact sheets.  This website is great to give specific advice on specialised diet, for example to increase iron or specific diets to help PCOS or IBS etc.

https://www.bda.uk.com/foodfacts/home

A useful website giving advice on some common childhood conditions and a symptom checker

https://www.what0-18.nhs.uk/

Also with children a website called when should I worry which is a good guide of when to seek help for coughs, colds, earache and sore throats

http://www.whenshouldiworry.com/resources/When%20should%20I%20worry-Booklet_England-with%20111%20service_2016.pdf

For constipation and urinary problems in childhood try the ERIC website for useful advice

https://www.eric.org.uk/

Information on renal disease in childhood

https://www.infokid.org.uk/

Confused about PSA, this helpful leaflet can help with the decision making process

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/509191/Patient_info_sheet.pdf

Informative information leaflets on sexual health including leaflets on contraception and sexually transmitted disease.  However, importantly some information in discussing reproduction and useful information aimed at children to discuss changes occuring for children age 6-11, both boys and girls.

https://www.fpa.org.uk/professionals/resources/leaflet-and-booklet-downloads

Useful information on food allergy

https://www.allergyuk.org/information-and-advice/conditions-and-symptoms