Hi, we moved to Miami with our two young children two years ago and everyone has adjusted very well without dominating the Spanish language. It will be an opportunity to pick it up though and children do so very quickly. Sometimes commute can be crazy so I would suggest you live and find a school within the same neighborhood, not too far from your work location. I do not know where you are coming from, but I am sure the children will enjoy the warm weather and being close to the beach. However keep in mind that July is one of the hottest months in Miami and hurricane season begins. Expect rainy days and hot humid weather. Starting late October until late April, it is paradise! Hope this helps:)
How exciting to receive a 2 year contract to work in Miami! Although Spanish is prevalent in Miami, there are many families who move here that only speak English. I have found that children adjust quite well, and will learn also pick up the Spanish language quickly.
As far as the right areas to live, it will depend on your home requirements, schooling (private or public?) and desired commute time to work. Pinecrest, Coral Gables and Coconut Grove are known to be attractive family neighborhoods.
I have lived here for 10 years, and relocating people to Miami is what I do. Would love to chat with you more to see how I can help you find the best community and schools for your family! For more information http://www.miamiglobalrelo.com/.