To do the top part of the dresses I used the same method as here. For the baby one I did the same idea but had to cut a neckline and sleeves.
I did add a little bit of the flowers to the top of the dress for my older daughter and added a bit of a scrunch in the front of the baby's dress. Otherwise the process was pretty much the same. Instead of hemming the sleeves and the neckline for the baby's dress I added a binding.