Dubrovnik and Islands in August

Hi

we are traveling to Dubrovnik in August : 2 adults, a 10 and 9 year old. We have booked an apartement in Dubrovnik old town for the first week to chill out and checkout local attractions.

For 2nd week we are thinking of one of the local islands where we could book acomodation, water activities, sailing, etc for the kids. We are quite flexible on catering, etc providing there are some reasonable restaurants close by. Any experience or suggestions on location, activities, etc gratefully accepted? Should we book accomodation and travel to island in advance?

Thanks