Here the eyes aren’t tack sharp
Awww, your little guy looks to be about the same age as my son.
I plugged your photo into an EXIF viewer, and here were the results...
Camera: Nikon D5000
Lens: 50 mm f/1.8
Exposure: Auto exposure, Aperture-priority AE, 1/320 sec, f/2.2, ISO 2000
Flash: none
Focus: At 1.0m, with a depth of field of about 3.3cm, (from about 16mm before the focus point to about 17mm after)
Date:
December 23, 2017 12:37:04PM (timezone not specified)
(19 hours, 26 minutes, 42 seconds ago, assuming image timezone of US Pacific)
File:
1,000 × 664 JPEG
97,877 bytes (96 kilobytes)
Color Encoding: Embedded color profile: “
sRGB”
It's a depth of field issue. You aperture is too wide, and as a result, you only have an inch "slice" of your subject that is in focus. If you miss the focus by a hair, you'll have sharpness issues.
I'd stop down a bit...probably at least to F4.0 It'll deepen your DOF so more of your image is tack sharp.