Your images both suffer from excessive noise, created by the very high ISO setting you used (12,800). This causes the photo to look out of focus and pixelated. For best images, try to keep the ISO below 800.
You might wish to review the exposure triangle, so that you may understand the relationship of ISO, shutter speed and aperture: What is the "exposure triangle"?
In your case, you may wish to reshoot, but set the ISO to 400 or 800, open the aperture to its maximum (3.5 hopefully with your lens). Depending on the movement by the child, you may need to keep shutter speed above 1/250th or so. A flash might be helpful.