Hi Matt
I have some experience in this area.
Babies are soft, light them softly - is my mantra with this subject (well Joe McNally, but I listened)
Also I am fond of using the macro lens for the teeny details, then creating a collage of those images.
Keep them warm & fed goes without saying.
If they do go to sleep - then it's a good idea to have 'white noise' going continuously, to disuse the sound of the shutter when that goes off.
e.gs attached - hope Im not too late
http://i64.tinypic.com/20urbiu.jpg
http://i66.tinypic.com/15frudt.jpg