Staff members can ‘use’ first aid certificates already obtained (these should be checked that they are in date and what the training covered eg. in line with the Emergency First Aid at Work requirements). It is likely that a pediatric first aid course would be adequate if this also covers adults/ EFAW this information will be detailed on the certificate or in the appendices. However if this is not clearly detailed then an Emergency First Aid at work is an appropriate course to attend this should be arranged locally.
If you need to attend a course this should be arranged locally. There are lots of providers but if you are struggling to source a course the red cross run Emergency First Aid at Work regularly in lots of areas - https://www.redcrossfirstaidtraining.co.uk/courses/first-aid-at-work-courses-uk-mainland/scheduled-courses/emergency-first-aid-at-work/