I just saw your message. I wanted to send you a reply rather than having it posted but couldn't figure out how to do that. Anyway, A great point of departure on the ethnography of babies is Alma Gottlieb's "The Afterlife is where we come from." It's very good if you haven't read it. On voice, that's hard because it's so plentiful. James Clifford, Talal Assad might be good figures to start with.
All the best,
PS How did you know I was planning to do research on babies?