Children are amazing subjects!
Bring yourself down to the child’s level, even if you need to get down on the floor. This view won't distort their image, as taking the shot from above will.
While posed shots are great, you can get better results by capturing an image when they are preoccupied. ie: while at play. You’ll capture their faces enjoying the moment.
Children who have grown up having their photo taken will be less likely to show off or not wanting to be in front of the camera Filling the Frame
Almost any shot will look better if you take a couple of steps closer to your subject. Filling the frame with your subject will make a big difference of how your images will look.
Instead of moving closer you can use your zoom in on your subject to get a closer shot. Fill the frame with your subject's face only. With less clutter in the image, there's less to draw the eye away from the subject in your photo.
If you can't get close enough when you capture the shot, you can zoom in later on the computer - crop out everything except the subject's face and see the difference it makes.