I know I've seen pictures of infants in bicycle seats (see
here,
here,
here,
here, and
here), but I haven't been able to find any models designed for infants. I've heard that in other lands, carrying a child in a sling or backpack is common, and I've seen it done here too.
I haven't been able to find the picture I have in mind, but if I remember it correctly, it was a seat in between the front handlebars where a baby could lie down.