Just FYI, here is a good pattern for a hand-made Sofia dress, one that is a bit simpler than the original, but very similar:
http://butterick.mccall.com/b3350-pr...hp?page_id=376
The pattern even includes a scalloped hem, though there are more scallops on the pattern than on Sofia's "official" dress. (It isn't really all that difficult to change the pattern to cut them down to four, however.) The simplest way to create the double skirt is to cut it twice with lavender and white fabric, and only scallop the outer layer. However, if you want to keep the skirt to a single layer to make it cooler to wear, another option is to just cut a strip of white fabric about 10 inches wide and hand-stitch it under the scalloped edge of the primary hem, so that it shows. (Or, if you REALLY want to simplify, you could also create the skirt's scallops by painting them on with fabric paint.)
I would suggest skipping putting on the peplum as a separate piece, and just use an outline of soutache braid in the same color to fake it on the skirt. Most kids really don't realize that the peplum is supposed to be an extra layer, so it works fine and minimizes the heaviness of the dress. The star patterns on the skirt can be done via applique or painted on with fabric paint. If you make the dress in a lighter woven fabric, painting works nicely.
Pearl beading can be purchased by the yard. The easiest to apply is the sort that is called pearl piping; it is mounted on a sheer organza ribbon and can be put on by machine using a zipper foot; you place it underneath the hem edge and topstitch it down from above.
http://www.laceheaven.com/p-12417-3-...rl-piping.aspx