I think a GREAT fun trip for the adults and kids would be to fly to either DC or Boston then take a train up and down the east coast visiting DC, NYC, and Boston.

Also, there are cruises that do this trip which could be fun and take some of the sting out of the humidity PLUS it is a fun way to travel.

http://www.princess.com/learn/destin...ruises/ncn.jsp

This one does NYC (embarkation but I would certainly add days at the end or begining of this trip)

NYC
Boston
Bar Harbor, Maine
Halifax, NS
Quebec City.