Jordan you are very brave! I used to take school parties to France and I can guarantee you a lot of sleepless nights especially if they like the odd beer or more!!

Around Barcelona - the Olympic Games sites (you could take them swimming in the pool), the various Gaudi buildings including the Sagrada Familia (a marvellous work, that sadly I may never live to see completed) and the Parc Guell, the Pueblo Espanol (a 'viilage' comprising copies of the most famous buildings in Spain with craft demonstrations), the Nou Camp stadium tour for all football fans, Monserrat Monastery, the Dali museum at Figueras and I'm sure there's an icerink and cinemas.

I am sure that you can enter Spanish School Holidays in Catalunya in a search engine and get dates, but as for accommodation, sorry I can't help you on that. Perhaps there's a youth hostel or backpackers accommodation, but I think you'll have to wait until someone more expert comes along.