Ok, for the 12-24 Month size dress, her are the specs. Your rectangle of fabric should be 16" wide x 19" tall. The armhole will be 3"(across) x 4"(down). Then sewn as others. (pattern link in sidebar)
One thing to note about the smaller dresses, you will only need 5-6" of elastic for the neckline casings and one package of bias tape is enough to make two dresses...just cut the package length in half twice.
I'll post finished pics and encourage you to do the same! :)
I also have another exciting dress surprise to share soon....can't wait! Stay tuned...