An earlier comment about Siena - I think it would be highly unsuitable on the day of the Palio itself - just google Palio to see how many tens of thousands of people cram into the Campo. The days before the palio might be interesting.

Another trip worth considering is Arezzo - about 90 minutes by slow train.

My daughter reminded me of something from our trip to Italy when she was almost 13.

We went to see the Last Supper in Milan. It was a really hot day, and the kids were crabby about going anywhere, doing anything. But from the moment we walked through the entrance and began reading about the damage, the restoration and the technology used to secure the masterpiece, my daughter was hooked. She asked a million questions and when we exited she wanted to go back to the beginning and see it all again. When the school year started and she found out she'd be required to create a science project, she immediately said, "The Last Supper! Humidity control! Human CO2 emissions!" Wow! That was time (and money) well spent! She got an A-. (Not that I'm bragging or anything.)

From reading your other posts I see you are also going to be in Rome and Venice on the trip. You might want to stop in Orvieto for an overnight stop on the way from Rome to Florence. You could also consider trying to add another day to the Rome portion of the trip

From Florence the day trips I would recommend would be Fiesole (very close, basically a suburb), Pisa and Lucca

I also agree with other posters that you and your husband should think about taking turns to see the museums without the kids if these are a high priority for you.

I have also read about but never visited the Leonardo da Vinci museum in Vinci--sounds as though it might interest your boys
Same goes for the Institute and Museum of the History of Science right in Florence
http://www.imss.fi.it/museo/index.html

Thank you to all for your help. I certainly have a lot of ideas. We don't want the whole trip to revolve around the kids, but we do have to be realisitc and break things up a bit. We do have some helpful suggestions. Thank you.

Siena would be a nice day trip. It is only a little more than an hour by bus from Florence and is an interesting walled city with lots of narrow streets and shops to explore, a wonderful campo and beautiful Duomo.

I have spent several months in Florence over the years and never grow tired of it. I generally include Florence on each of my trips to Italy and will be spending a week there in October in between visits to Milan and Rome.

Shooping has become an expensive past time though the kids might enjoy the street markets. And it is likely to be very hot and muggy in August.

Have you considered a hotel with a pool? The kids owuld likely lok forward to a bit of exercise and cooling off in the afternoons.

For me, packing up to make a short trip and spend one night is not worth the time and effort and I would assume that would be even more so when kids are involved.

There is a museum of medieval torture that might appeal to your boys and be a bit different from the art, etc. And they may also enjoy the leather school, which is free and interesting for an short visit.

Something different that might also be interesting is a visit to San Miniato for vespers. It is jsut lovely and perhaps would appeal to your boys as well as you and your husband.

Florence is my favorite city in Italy and I could happily stay there and not leave for weeks, months or years.