Even with all the trouble in Mexico, I'd rather send my kids to Cancun and it's just as cheap as Jamaica. There's a much larger tourist/resort area and less hassle on the beach. I can't imagine 20 year olds staying on resort property for more than a day or two, their curiosity will get the best of them. In Cancun, there are many places they can go, be safe, and be off property. JMHO.

