Definitely visit South Beach, but if you have kids with you, Miami Beach is perfect.
I like to stay at: http://www.fontainebleau.com/
They have multiple swimming pools, some of which are indoors, and the restaurants are good inside the complex.
Dining for Cuban food, I recommend going to Little Havana, the restaurant there is called La Carreta. Don't forget to order Mojito drink
5350 West 16th Avenue Hialeah, FL 33012
show us some pics of the places you visited in Miami!