Hi Sarah
From what I can gather, tour operator kids clubs are supposed to be exclusive for the kids on their package holiday IE: Thomson clubs for kids on a Thomson holiday, Thomas Cook clubs for Thomas Cook's clients. etc.
Thomson's kid clubs have specific age group clubs and the staff are all trained with some qualification regarding childcare, the equipment used will pass the British Safety Standards and they all will have had CRB checks, plus the ratio of how many kids to one representative is adhered to, although if they don't have a lot of kids to look after, they may allow kids from other TO's into the specific age groups, as long as the parents pay or stay with the child.

Hotel run kids club... anybody can join and the people running it may not necessarily speak English or (depending on the countrty) have had the necessary checks as above.

http://www.childfriendly.co.uk/family-package-holidays/thomson/family-clubs/
http://www.netmums.com/coffeehouse/house-garden-194/holidays-travel-emigrating-104/428872-hotel-run-kids-club.html

HTH's
Sanji