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I've booked to go on the Med Discovery and Spirit in Oct and hear that the Pompeii tour is good for the Naples stop and that your better off doing your own thing (cheap hop on/off tours are available) in Barcelona as the port is more or less in , the City Centre. Having been to Barcelona before if your children are sports fans the Nou Camp Barcelona FC tour is a must.
Never done a ships excursion in the Med. It's easy enough to do your own thing via taxis' bus or train and at a fraction of the cost.
We did this itinerary in May and used the Pompeii and Mount Etna with Taormina excursions, woul highly recommend both. The other towns we did our own things, Barcelona is very easy to get around as you dock almost at start of Las Ramblas. Depends how old the kids are, there are some beach excursions, or you can do your own.