The first thing you'll need to do is put your camera into P Mode. You'll find this on your camera dial as a P. Don't panic if your camera dial looks different to this photo, each brand displays the settings differently, but they usually all have a P Mode! Let me know if you can't find it!
P Mode gives you a little more control over your camera than automatic mode.
You may not know this, but your camera has a selection of focus modes to tell it if your subject is static, moving or being unpredictable (ie standing still one moment, then running the next!)
Some cameras have all of the options listed below, some have less and some have more! The key thing is to select the best option for what you're about to photograph.
Simply go into your camera's menu and chose the best option for your photo. Check your manual or ask me if you get stuck!
YOUR SUBJECT IS
STATIC & MOVING
Use this mode when your subject stays on one focal plane and doesn't move backwards or forwards. They can move ie wave, jump etc but cannot move forwards or backwards.
This mode is for when your subject is moving, especially towards or away from the camera and leaving the focal plane. The focus will act like a piece of elastic and move backwards and forwards with them as they move.
There will be times, especially with children when you don't know if they're going to stay still or move, so this mode prepares for all eventualities!
CANON: Intelligent Focus
SONY: AF-A Automatic