Hi pjbosjr.
I guess it all depends on what sort of traveller are you (and your son). Certain people like quantity (the more places, the more miles, the better) while others prefer quality (less packing/unpacking to move up and down and more getting to know a place beyond the 'obvious' tourist landmarks). I personally prefer the later. So if I'd have to plan something I'd choose an area, identify a base-city, explore it thoroughly and then do day escapades from there to nearby sites. No matter where you go in Europe, there are plenty of choices near big cities, same happens in Spain. Yet others will tell you that you can visit the whole Iberian Peninsula in 10 days! As said, it all depends what's your 'vibe' when travelling.
And of course, being myself a Barcelonian, I can't but recommend to visit this city and its region, Catalonia. It's no coincidence that over 12 million visitors from all over the world choose this region every year. A great 10-day trip could be: Barcelona (5 days) plus day escapades to Tarragona, Besalú, Girona, Montserrat and say Sitges. All of them are fairly close (less than 2h by train/bus) and would provide very different things to see: Tarragona was the old Roman capital of the whole most Western province of the empire still keeping many features (circus, amphitheatre, etc), Besalú is a 12th-century Romanesque medieval town (the real thing!, no reproduction or papier-mâché setups), Sitges is a lovable little coastal town, Girona is considered the second capital of Catalonia (Barcelona being the first one), and its Old City is well worth visiting, and Montserrat -aside from having one of the key monasteries of the Catholic world- it's an impressive mountain range that calls for a wonderful hiking day.
If any of these catches your attention let me know and I'll point you to different videos so you can 'taste' before deciding... boy, I sound like a bloody travel agent, don't I?... but I can assure I'm not, hahaha!
