Tom makes some good suggestions. I would also mention that the Diamond Princess and Royal Caribbean's Vision of the Seas do Mexican Riviera cruises round trip from Los Angeles (ports include Cabo, Mazatlan and Puerto Vallarta). Royal Caribbean, Celebrity and Princess would all be good choices for the age category you specify. However, please be aware that Christmas sailings are at a premium right now, with many ships already sold out. So you might want to act very fast.