This looks more like autofocus calibration error than motion blur or bad technique. In your example, the background grass appears sharper than the child, which suggests back-focus: the camera focused behind your intended subject.

Why it shows up:

• At 70mm and near maximum aperture, depth of field is shallow, so AF errors are obvious.
• The K10D is known to have back-focus issues on some bodies.
• AF points can cover a larger area than expected, so the camera may grab contrast behind the subject.

How to test it:

• Use a controlled setup: good light, a focus chart or angled ruler, camera on a tripod.
• Use a fast AF lens if possible.
• Repeat the test consistently under the same lighting.
• Check whether focus consistently lands in front of or behind the target.

What to do:

• Make sure the camera firmware is up to date.
• If tests confirm consistent back-focus, the body/lens may need calibration.
• The K10D doesn’t offer easy user AF microadjustment, but some users access a debug menu for adjustment—use caution.
• If you’re not comfortable doing that, service calibration is the safer fix.