Ciao Sue,
I'd recommend any and all of the places I linked in my post above - all are clean for sure, family-run and have showers. It is actually getting harder to find places with tubs. Most offer free wi-fi too.
If you're interested in a cooking class, you can inquire with any of them whether they will organize one for you... or you can contact the ladies at Kitchen Chez Nous (I'm linking to my interview with them
here) and have them come out to wherever you end up staying.
With a 12 and 15 year old, I'd highly recommend
Vernianello above.
A few more I'd add to the list are:
http://www.tuscanyaccommodation.com/tenuta-moriano.html
http://www.tuscanyaccommodation.com/borgo-della-meliana.html
These, along with Fattoria Il Lago (linked above), would be the "coolest", just because of their houses being on hills.... and they also have several villas divided into apartments that might be more to your liking (whereas some of the others are apartments within one single large villa).
All of them, being in the central area of Tuscany to the east or south of Florence, are within an hour from the Florence airport.
If you want to fly into the Pisa airport, you could also stay closer to the coast. I'd suggest maybe heading into the
Garfagnana valley, where at that point you have the mountains all around. Barga would be good, but if you have a car, any place here would be great. Actually, the Wind Cave might be something your kids might enjoy too. For lodging there, take a look
here.
You won't have problems with the food part, as all of Tuscany offers great cuisine based on local, fresh quality ingredients!