There are specific laws and guidance on protecting the vulnerable in society, which all health staff should be aware of. For guidance around children the NLH specialist library for Child Health is a good starting point.
The General Medical Council provides guidance for doctors on how to behave. It is the GMC that investigates allegations against doctors. Other professions also have guidance. The Nursing and Midwifery Council provides guidance on fitness to practise for professionals, as well as information for the public on making complaints. NHS Choices also advises patients on making complaints against the NHS.