Autofocus not cooperating can ruin a good photo session, tbh particularly with active grandkids. From my experience, start by inspecting the lens mount for any debris or misalignment; a tiny speck can throw everything off. Remount the lens firmly to ensure proper connection.
Next, test with a different lens if you have one, to isolate if it's the camera body or the lens itself. If it's the body, a factory reset might clear any software hiccups. I've seen that resolve focusing woes quickly. Persistent issues could mean sensor cleaning is needed, but handle that carefully or seek pro help. Should get you focusing sharply again soon.
