Delia from Delia Creates shows how to make her Suspender Dress for a baby girl. The bodice and straps are made from a stretch knit for an easy fit. You can make the skirt from the same fabric (as shown here), or use a contrast-y fabric. For a size 3-6 month dress, she was able to get enough fabric to make the skirt out of a single fat quarter. Get the tutorial at Delia Creates.
[photo from Delia Creates]