Okay, so guess what! This was the first critique request that I saw since I decided to start doing them - yay for you (^ ^)
That said, you have a well developed style going on. The attention you give to certain parts ("Mary's" socks, the characters' hair, the little "cope" on the more grown up Jesus) is admirable. The linework works well with the subject matter and style, and really I have no complaints with the character designs.
The only real problem I have with it is that there's a lot of unused space in the top right corner. Maybe you could have drawn in something else up there, like a monogram or a cross or something. Or possibly reorganising the characters so that they're closer together would have done well too. Also, the way the feet cut off at the bottom...
But other than that, I'd say it is a pretty successful illustration