The only innoculation my doctor has ever suggested is Hep (I believe it was "B") since I do visit Playa on a regular basis (although we've never gotten sick from our Playa trips, but we did get very sick from a visit to Punta Cana, Dom. Republic in 2002). The Hep innoculation consists of two shots, 6 months apart, so you're probably too late to benefit from it at this late date (don't know if the first shot helps without the second one but I'd guess it couldn't hurt - no pun intended).
I'd say give a call to your doctor for you and your hubby and contact your children's pediatrician to see what he suggests for the kids.
Have a great time in Playa!!!!!