I made this dress for my granddaughter's third birthday present. I bought the shirt at Walmart. It had a double ruffle on the bottom of it. Took a jumper pattern in her size (that I've used before to make a jumper). Found the waistline and cut off the shirt with 1/2 inch extra for a seam allowance.
Then I strip pieced apple green, pink and lavender quilter's cotton prints. When I had enough I cut out the bottom of the jumper pattern (from the waist down); leaving 1/2 inch seam allowance at top and bottom.
Next I cut out the skirt liner. What I mean is I took one piece of fabric and cut out the skirt pattern (ended up with a back and front). I did this because I thought the pieced seams would be rough on a child's skin. So I put the pieced front and the liner together, rights sides to right sides and inserted one of the ruffle pieces; sewed the seam. When it was sewn and fabrics turned right side out, the ruffle (that had been on the bottom of the shirt) was now on the hem, tying the two together. At that point all I had to do was sew front to back and then attach to the shirt.