There are no legal requirements for the staffing levels at a Kennels. Local Authority guidelines (they issue licenses for dog kennels) seem to state a minimum of one! They say "A fit and proper person over 16 years of age must always be present on site to exercise supervision and deal with emergencies whenever dogs are boarded at the premises.
Dogs must be visited at least three times per day to check on their health, safety and welfare."
I looked for a link listing these guidelines but only found this one ... which is worse as it just says "A fit and proper person should always be present to exercise supervision and deal with emergencies." and doesn't even give a specific minimum age:
This website lists the legal requirements of a boarding kennel: