Sounds like us (and probably a lot of families to be fair). Holidays that have been good for us are:
Malaga: Hired car, stayed at Molino de Santillan, Marachariaya. Visited Malaga for Picasso museum, castle, Alcazaba etc. Beaches at Rincon de la Victoria, Burriana beach at Nerja (went to caves at Nerja as well). Tivoli at Benemadena, also took cabel car there too.
Pamplona: We stayed with a friend when the festival was on. We didn't take the kids to see the bulls but they did enjoy the rest of the festival and exploring the local area.
Corfu: We stayed not that far from Corfu Town in a hotel we got cheap on Lastminute.com. Spent day in Corfu town, visited Archillion Palace, Byzantine Museum, also went to a monastary. Obviously beaches and there was a waterpark.
Amsterdam: All the art galleries obviously. Stayed at Eden Hotel, not very child friendly but fine. Kids liked the bontanical gardens and cancal cruise. Took them to Ann Franks House etc.
Paris: Did the sights like Arc de Triomphe, Eiffel Tower, ouvre, Pompidou Centre, Notre Dame, Jardin d'Acclimatation and did 2 days at Eurodisney.
Belgium: Stayed in Roche en Ardenne. Visited castle, lovely walks, pretty town. Took kids to parc chlorophyll. On way home went to Lille for day. Lovely city, good for kids, free zoo, nice parcs, museums, citadel.
Next stop Venice but we are Eurocamping! Am hoping to spend a day in Venice, just walking about and taking in the sights, another day visiting Murano (not whole day), another day at Aqualandia and rest of time exploring local area and kids having fun on campsite.
To be honest, we do take the kids round museums, tourist attractions we want to see as it is our holioday too! We do try to arrange it so that we can blackmail them all the way round that we are going to go somewhere kiddified after....
HTH