We just spent a wonderful week in Tuscany, and one of the highlights was staying in Casale di Villore. It's a gorgeous property with stunning views of rolling green hills, olive trees abound, and the pool is also beautiful (even though it was too chilly to use it).
We were there with our two-year-old son who loved running around, playing with the rocks and looking at the pool. It's a quiet, lovely place where you can listen to the birds singing all day and watch butterflies flitting about. We stayed in the Granaio apartment, which was more than perfect for all of our needs. It was comfortable, spacious, and when we needed to use the heater, it worked very, very well. The kitchen is great, and we enjoyed our apperitivos and dinners while watching a gorgeous Tuscan sunset every night.
Poggibonsi town has everything you need for groceries and other things (we needed to have our car looked at while we were there), but it is a bit of a drive away (15 min or so). I would say a car is a necessity. Antonio was also so helpful, answering all of our questions and giving great recommendations. We would happily return any time.