The NSPCC defines safeguarding as actions taken to promote welfare and prevent harm.
A child is anyone under the age of 18.
As a volunteer for Medics&Me, you will be mentoring children and you need to be aware of how to spot potential harms and dangers to the welfare of your mentees. This includes, but is not limited to, recognising signs of abuse, acting on suspicions/disclosures and acting appropriately around your mentees.
References
UN Convention on the Rights of the Child
NSPCC - Getting Started on Safeguarding and Child Protection