Broad-winged chicks

Much to my surprise I discovered these chicks in a nest right across the road from my house. I had noticed the female had been flying around the back yard recently and so I followed her around to the front of the house and she took me right to her nest. The nest is about 50 ft high and I was about 30 meters from the tree. I took the image last Monday, and although the chicks are not flying I have no idea just how old they are. If someone has an answer/guess to age I'd appreciate a note in your comments. I'll note that I also used an extension tube (12mm) for the first time in hopes of bringing the subjects closer.

Thanks for taking a look.

D300
300mm f/2.8
TC-20E II
1/640sec @ f/8
ISO 640
EV 0
Matrix