There is one major misconception about photographing children. People think children have to smile to make it a great image. Some of the best pictures I've ever taken of my kids have no smiles. I actually try and tell them not to smile. The more you have the camera around them, the more they get use to it, and the sooner they forget you're behind it. Get them playing when they aren't looking at you. They will be the images you will frame and hang on your wall. Try and get them when they first wake up, or after dinner on a full stomach. For my children, the "witching hours" are between 7 and 9. You know when your children are the brightest and most even tempered. Pick those hours.