Hi Stephen,
We took the Mediterranean cruise in May 2010. It was a fabulous voyage aboard the Disney Magic!
We spent one night pre-cruise and two nights post-cruise in Barcelona. We were absolutely exhausted from the air travel so the first day we didn't do any touring. We did walk over from our hotel to a nearby mall (Barcelona Glories) to eat and look around at some stores. It was a fun indoor/outdoor shopping center. Otherwise, we mostly slept prior to getting on the ship. At any rate, before we boarded the Disney Magic, we were well-rested and ready for the port-intensive voyage!
Upon our return to Barcelona, we used the Metro system to tour the city. We saw the Sagrada Família church, Park Guell and the tree-lined pedestrian mall, La Ramblas. In the evening, we went to The Magic Fountain of Montjuic.
On our final day, we had plans to take the train to Montserrat but we were toured out and chose to head to the beach instead. We had wonderful hot chocolate and churros too!
If you are looking for a tour, Disney Cruise Line offers some
fun options pre and post cruise including a half-day tour of Montserrat or a driving tour of Barcelona.
I wish your family a memorable voyage!