Children can sometimes be a challenge in technical terms, as they are small, low down, and move very quickly. They usually require stamina and fitness on the part of the photographer, as well as quick reflexes. You can help yourself by trying out these techniques:

With very small children, work at a fixed distance: focus your lens manually to, say, 0.5m (18 in) and keep your subjects in focus by leaning backward or forward as they move. Small children move very quickly but usually only over short distances. This method requires little effort and can be superior to relying on autofocus.

When you first photograph a group of children, fire off a few shots in the first minute - they need to get used to the sound of the camera or light from the electronic flash, while you need to exploit their short attention span. Once they have heard the camera
working, they will soon lose interest and ignore you. If, however, you wait for them to settle before taking your first picture, they will be distracted by the noise.

For professional photography of children, the best cameras to use are SLR-type digital models or manual film-based cameras. These give you more flexibility than ordinary digital cameras or autofocus compact types. You need the shortest possible shutter lag (the time interval between pressing the shutter and actually recording the picture) if you are not to miss out on the really spontaneous images.

In low light, try using faster film or increasing the photosensor's sensitivity rather than setting the lens's maximum aperture. With non-professional lenses, you lose more image quality through using large apertures than from the grain given by higher-speed recording.

In the end, keep in mind that these kind of informations are easy to be found on internet if you are interested in learning more.