The first thing that strikes me with this picture is the eyes and the emotion emitted from their expressions. There is a magical peace here, The softness in their faces really make me feel very comfortable and brings a smile to my face.
I really like the way the older gentleman is crouched down more than the younger one, he make an invisible line that moves the viewer from him to the younger one with the brighter expression. The direction of their gaze also continues to lead the viewer. The position of the older mans arm is a great touch. It give me a sense of framing or completeness to that area.
Like many have said in other comments, it is a bit flat. The grey tones seem to mute both subjects from the background. Increasing the contrast might help here. The younger mans darker hair gives you a good idea of how a more contrast can really power this up.
The lighting is perfect in my opinion, no harsh areas and the focus is also good.
Its a very good picture overall and after reading your comment behind the picture, I can see how much more precious this is.
The expressions on the mens' faces is great. It might help to have a little more contrast, the color range seems pretty limited. Also the gray background is too close to the gray on the men's skin and clothing. You might bring them into greater contrast with a different color (white maybe) background.