Here are some baby photos from the 1800s, that were mixed in with an envelop! I don’t think that the baby photo, by St. Louis Photographer Bell Studios, came in the envelop as it’s postmarked from Miss A. Schenkel in Detroit (and sent to Henry Kellogg St. Louis). Whatever correspondence it once contained has been lost. The baby, presumably E..? Warren Kellogg, looks rather crazy in the eyes, giving that unfocused gaze just past the camera.
The other baby is on a plain, unmarked, cabinet card and looks a little more recent.