Morocco. Beaches, Great food, Mountains, plus Spain is 45 min. by ferry
Moroccan food is terrific, people are friendly, and the mint tea is the bomb diggity bomb. If you enjoy bargaining (I love it) you'll come home with a quality rug or two, shipped directly to your door back home.
There are loads of cool things to see and do, your kids will come home with an appreciation of a really unique culture, and their first-person experience in Morocco will dispel lots of common myths about life in North Africa.
My family (kids age 17, 15, 13) loved Morocco.