C., the last I heard about flat feet and babies was that you shouldn't worry about that. It takes time for the muscles of the feet to develop, so it's too soon to tell if he's flat-footed or not. There is also a theory that most flat-footedness is actually CAUSED by hard-soled, flat, ultra-stiff baby shoes! You know, the kind that they usually have bronzed! The best advice I got when my son was a baby is to allow him to be barefoot as much as possible so that his feet can develop naturally -- being barefoot allows the full range of motion in the feet, and so the muscles all get a good workout. Unless there is a deformity in his precious little feet, you shouldn't have anything to worry about.
When you do have to put shoes on him, make sure they fit him comfortably and allow him to use his feet without constricting them. Sneakers are good for this. Again, those awful little hard shoes that encase the whole foot can actually cause problems with foot development. My advice is to not put any shoes on him at all unless he needs them to protect his feet when he's walking outside.
I hope this is helpful!