There are a few simple steps to successful child photography besides the usual photographic skills. Take the photograph from the childs level. Be quick and decisive with the camera. If possible, plan your photograph in advance and have everything ready. For outdoor photographs or shots using available light, use as fast a shutter speed as possible.
Children move frequently and quickly, often becoming a blur in a photograph.
Make taking a child's photograph fun. Make a game of taking their photograph. Have them play acting or let them dress up. Under no circumstances show a loss of patience with a child or force them to pose when they do not want to. Outside of the moral issues involved, you are never likely to get the image you are looking for in this situation.