I made a knot dress for my daughter using Simplicity pattern 2171. The pattern was very easy to use. It won't fit my daughter until next spring thou. I still don't understand very well how children measurement works. I measured my daughter waist and chest and decided I should go with a size 3. It runs a little bit big on the chest and I did not made adjustments because I would ruin the bodice part. Anyway, the dress turned out to be gorgeous.
This pattern is one of the most populars right now. Moms are using it to create "Matilda Jane" look alike knot dresses and I have seen a few dresses selling at Etsy for over $35 which I am pretty sure were created using this Simplicity pattern. My advice, if you can sew and like the look of this dresses go buy some Calico fabrics and you will love the results. I hope to sew more of this in the future.
Here is the dress I made. I picked up some Calico fabrics and tried to copy the one in the picture. I also made the ruffled pants which I altered so that she can wear them this fall. I will be posting pictures soon.