Most cruise companies won't look at applications for employment from people who haven't got a minimum of 2 years relevant experience in the type of job for which they're applying. Competition for jobs is tough and (compared with, say, stewards) there are very few childcare jobs. (Most cruise operators target their advertising at 'mature' people, so there aren't many children on board).
There are dozens of books which offer advice on getting jobs on cruise ships; check your local library. There are also hundreds of wesites which claim to be able to get you jobs on board the ships; personally, I wouldn't bother with any of them.
So, what should you do? I suggest writing some letters, mentioning your qualification, seeking advice on careers.
Try these addresses:
Fleet Personnel
Cunard Line Ltd
Mountbatten House
Grosvenor Square
Southampton
SO15 2BF
Fleet Training
P&O Cruises
Richmond House
Terminus Terrace
Southampton
SO14 3PN
Hoping this helps,
Chris