Just a thought to add to the mix. It is possible that the child/angel in the picture represents a child that passed away before the painting was completed or even comissioned. As a mother of a daughter with Downs (a.k.a. T21) I can see the features clearly in the painting, although I wish I could see a bigger version. Since the painting was completed in 1515, obviously we can only guess, but regardless of the meaning or specifics, it is intriguing and frankly endeering to see him/her portrayed.