Molly is wearing the dress inspired by the one she wears in her "Meet Molly" book.
It has a peter pan collar, a sash that ties in the back, and adorned with real mother-of-pearl buttons.
You can also see Izzy wearing it below:
This dress below that Izzy is wearing is a classic look accented by a ruffled collar trim and a cream waistband. Doesn't she look so polished?