Some of our best family adventures overseas (& one local):
Tokyo is excellent - Edo Museum, Disneyland, Mount Fuji close by, food yum and excellent public transport (airbnb accommodation though to avoid $$$.) (Osaka has Universal Studios and a massive Harry Potter theme park and close to Kyoto.)
Siem Reap Cambodia - great food, transport (tuk tuk,) temples and hotels are affordable.
Hong Kong - Great food, public transport excellent, Disneyland, Waterpark, shops, parks and boats around to little islands.
Singapore - Commercial, clean, friendly, convenient, Universal Studios, parks, interesting districts, yummy foods & close to Malaysia/Indonesia for quick get aways (Tioman is stunning.)
Kota Kinabalu - great hotels, food, trips, scenery and only a hop and a skip from Kuala Lumpa.
China - Shanghai - international bubble, Beijing - forbidden city & great wall, Xi'an - warriors and lots more to see (5000 yrs of history), public transport excellent (high speed railways) and food delicious.
Netherlands - Amsterdam - fun, Efteling - theme park and good food.
Paris - great museums (D'orsay, l'Orangerie, Picasso - figure out how to queue jump with advanced purchase tickets,) disneyland/disney studios, food fantastic and nice getting a water boat.
London - British Museum, V&A (courtyard paddling pool with little ones splashing about & adults sipping chilled white wine might be one of the best things to do on a summer's day) , Natural History Museum, Harry Potter experience only 40 minutes away, food good & diverse.