One more thing to rule out is motion blur masquerading as bad autofocus - kids move so try shutter speeds around 1/250–1/500 and raise ISO or add light; stabilization helps your hands but won’t freeze the subject. For grandkids, use continuous AF (AF-C/AI-Servo) with a single focus point on the face and enable the AF assist lamp and focus priority. Also try a different lens and reseat the current one; if another lens focuses fine, you’re likely looking at a lens-specific calibration that AF fine-tune or a service can fix.
