The best vacations for families by far are cruises. Depending on the $$ you want to spend you can get a sweet 3-4 day or 7 day vacation. There are very little down sides to taking a cruise.
1. Unpack once.
2. They have staff on board that takes care of your family and maybe 2-3 others durring the trip.
3. Food is aways available and included in the price. (except alcohol)
4. They have tons of stuff to keep your kids busy and out of your hair for most of the day, so you can have a vacation too. Most ships have a casino on board.
5. You get to do day trip to some pimp places.
A few tips:
Get currency for the places you are going, but they all take american dollars. Just so you don't over pay for some little tourist trinket or for a cab ride...they don't give change. Basic spanish is very useful. Most people do speak english even if they pretend not to. Make sure to hit the "duty free" stores in the airports and on the island. Cool stuff is alway better when it's cheaper.
Meg