A lovely photograph, but would love to see it larger.
Composition / Content
Composition is nice here. The off-centering really works, giving the photograph some depth. You've cropped the child's face nicely, although perhaps leaving the full chin in could have given more depth to the bottom of the image (showing the fall to the neck/chest.) The child himself is presented warmly, although the smile looks a bit forced, which is common. Sometimes presenting a look without a smile, if it seems more natural, can really help the mood of a photograph as well, but that's just a thought for the future, the smile does play well here.
Background
Nicely out of focus, and not cluttered, it adds to the feeling of depth around the face. As mentioned, I would have liked to have seen more at the bottom of the photo.
Camera Work - Technical
This is a very nice photograph technically. Nice exposure, good DOF, great focus. I think the eyes could have used more light, which could have been accomplished with a reflector or a reflective type surface.
Digital Processing
While your clarity is great, and contrast seems good for the background, I think that a little more highlight in the facial features and the eyes would have helped a bit. Maybe not so much on the facial features, but definitely in the eyes. Bringing the irises out would give the photo a great feel. I see that you did dodge the irises a little, but I think a bit more would have done wonders. Your neatimage work is good, I didn't get the feeling of it being over-smoothed, and there is still some nice texture in the skin.
Fits the Challenge
Hard to say that it doesn't fit the challenge, as I've seen many calenders that stick to subjects like this. I feel that the monthly connection is a bit weak, but that's entirely subjective.
My Opinion on the Photo
As mentioned, with a few minor tweaks, and perhaps a slightly larger presentation, this would go good in a calender of like images. It's a wonderfully warm and emotive photograph on it's own, and will be cherished by you and your family I'm sure.
If you care: The song that is playing on my computer is "Song to the Siren - Did I dream?" here's a link to the lyrics //www.open.hr/~dalbor/tmc/lyrics/siren.html
I only am posting this becasue I believe that every wonderful image has a song it belongs too.