With only one week I would consider Costa Rica for many reasons: good medical health care, many people speak english, really safe in comparison to nearly every other Central American country and it is so small that it is easy to see quite a bit of the country in a short period of time and - depending on your children´s favoured activities- easily accessible beaches and great national parks.
I travelled there alone as a 20-year-old and never felt even the slightest bit endangered.
Have fun planning the trip.