They need to have Common Core Skills & Knowledge at a minimum. It is a one day course, or can be done via distance learning.
When Ofsted carries out an inspection, the inspector will ask to see evidence of meeting the registration criteria. If the certificates for course, insurance, paediatric first aid cannot be produced or only some of them produced, they will issue a failure on the inspection report and set a date by which the relevant certificate must be produced (probably within a month). If that is not met, then they may take action to deregister from the scheme.