Originally posted by haviet What I did was I focused on the kid's face, and after I got the focus locked, then I move the camera in the same direction as the kid was moving before I pushed down on the shutter. Is this the proper way?
If you do it that way there is a good chance of getting out of focus shots if the subject was moving either towards or away from you.
Depth of field (DoF) is your friend here and you need to shoot with a fairly high f-stop number in order to get a larger DoF. Pre-focussing on an object about the same distance away is also a good idea so that you can take the shot when the subject is in the focused area. This also means that you have to disable (either temporarily or permanently) the half-press auto-focus feature on the shutter button otherwise the camera will try to re-focus when you press the shutter.
You could also set the camera to AF-C so that it constantly adjusts the focus as the subject moves but you need the half-press auto-focus to be ON in this case.
The technical term for moving the camera in the same direction as the subject is 'panning' and it takes a lot of practice to get it right. You have to marry the movement of your hands to the movement of the subject. A higher shutter speed will also help to freeze the action. A good way to practice panning is to go to a local park/playground and photograph your kids (unfortunately in this day and age people get upset about photographers photographing other people's kids in playgrounds) on the swings first and then on a roundabout/carousel. The swings will constrain the movement to a single plane so that you can pre-focus and then practice panning while shooting from the side, the roundabout/carousel adds an extra dimension of difficulty as the subject will move towards you and away from you as you pan. Again a large DoF and a high shutter speed are your friends here.
Bear in mind too that the combination of a high f-stop number and a high shutter speed will need a LOT of light or alternatively a higher ISO number (which can introduce 'noise' into the shots).
Practice is the key and you will get better at it, the trick is to start with easier situations and build to the more complex ones.