The gite we stayed in was in Bourgogne on the other side of the Loire, about 20km to Sancerre. It was remote and no, not a great deal for kids unless you were willing to get in the car every day.Dh and I went on our own for a week of total collapse.
For the chateaux you will need to be close to Tours, Orleans, Blois or even Angers.
We stayed near Doue La Fontaine on another occasion and were able to see Villandry and Azay le rideau castles and to visit \link{ www.la-recreation.com\La Recreation }which was a fab day out for dd when she was about 5.It's a fun park where all the rides etc are made form recycled rubbish. Fab!
Tours is a beautiful city in itself and might be worth a look.Vouvray is also very pretty. this looks nice