We will be in Delft for three days in October. We would love to go to Belgium. I would love to visit Ghent and/or Bruges. Is this doable. I will be with my husband and two daughters ages 5 and 8. Should we take train, rent a car, or hire a guide?
Take the train - should be very easy, with one train change at most. You may not want to walk from the train station in Ghent and/or Bruge to the center - you could either take public transportation (bus or tram) to the center or a taxi, I guess.
Best is to keep a question to ask limited to one country, I have posted my reply under the Belgian section.
Assuming this is meant as a day trip, getting to and from Brugge or Gent will take a large chunk of your day, with travelling times around 2,5 hrs if not longer. Better have something closer by.
If the weather is fine, the Waterbus - the river ferry between Rotterdam and Dordrecht - would be a nice way to get to the windmills of Kinderdijk.
If your children are into dinos and assorted stuff, the natural history museum Naturalis in Leiden is the place to be with an original T. Rex. And afterwards maybe a boat trip through the canals.