AF-A is not dependable if you want a specific object in focus. I don't know what the algorithm does or is supposed to do. It seems to me that it picks the most "prominent" thing in the scene, whatever that is.
But anytime I want a face in focus, I use single point focus & exposure. Then move the focus point as needed to focus exactly on the eyes. Yes, this can be difficult with a child. But it will get you a better % of properly focused and exposed photos.
working on it in Middle TN Nikon D3100
35 mm 1.8 Nikkor 18-55 mm Nikkor VR 55-200 mm Nikkor VR 55-300 mm Nikkor VR 150-500 mm Sigma OS MeFoto Road Trip w/Q1 ballhead Feisol CT3471 & Markins M20 ballhead