Six of us (inc one 3yr old) will get off cruise ship at 8-9am. Flight to Germany leaves at 8pm same day. Need suggestions on how to see some of Barcelona. We will have luggage.
Assuming they have a place to put your bags at the train station, I would take the hop on/hop off bus. It will give you an overview of Barcelona in the very short time you have.
Just be sure to be near the Plaza Catalunya when you are ready to depart for the airport. The Aerobus has a stop there. It's the best way to the airport without paying extra Euros for a taxi.