So far we have visited the USS Lexington.  Huge, HUGE ship ( I guess I haven't been in a ship this big).  Though I would not recommend going with a 2-yr-old.  People told us it would take us anywhere from 3 to 4 hrs to go through the whole tours they do- it only took us 2 to 3 hrs.  All my son wanted to do is run or touch every button or display while I ran behind him so he wouldn't destroy something valuable:)