When set to auto, some cameras can take a while to adjust for white balance and focus. This is the 2-3 second delay between when you first push the shutter button, and the shot actually being taken.
If this happens with your camera, try presetting these by holding the shutter release half way down to tell the camera to focus before you need to take the shot.
Then, keep your finger held half way down until you get the perfect shot, or use your camera’s ‘lock exposure’ feature to keep the exposure settings locked until you find the right time to shoot.
Presetting your exposure and focus can REALLY help out when taking shots of children. They tend to not sit in one place waiting for you to adjust your camera, so the best shots are taken when you are prepared for a candid moment – eg when the child is engrossed in a task.