Ho Chi Minh City
AItaly: Family of 5 in Italy - ideas or tips?
Bologna is awesome. Great food, not that crowded with tourists like the other cities you mentioned. even though they are probably more a must see from the tourist point of view.
AGermany: Places to stop in Germany between Brussels >>> Berlin >>> Amsterdam
Cologne is a good stop. As well as Dusseldorf. Düsseldorf is more beautiful, Cologne is more bustling. Hamburg is great. Don't do Frankfurt.