Now on to how to draft and sew a pocket.
Take a 8-inch long and 3.5-inch wide rectangular fabric (preferably of the same color as the collar). These measurements are for kids' sizes 2 and 3. For kids over these sizes, you may have to increase the length and width.
Fold it in half upward and mark 0.25-inch seam allowance on the sides and the bottom. Shape the bottom of the pocket as shown in the image.
Sew along the seam line.
Turn the pocket inside out, fold inside 0.25 inch at the top, and top stitch or whip stitch by hand (if you prefer).
Now pin it in place and sew over the sides and the bottom. Sew as close to the edges as possible.
Sew buttons and buttonholes on the center back of the dress and you are done!
Note: I preferred to have double layers of fabric for the pocket. If you prefer a single layer, take a 5-inch long and 3.5-inch wide fabric, leave 0.25-inch on the sides and the bottom, and 0.75 inch hem allowance at the top, shape the bottom of the pocket, hem the top, turn under the 0.25-inch allowances on the sides and the bottom, and pin the pocket to the dress and sew. The pocket measurements are for 2- to 3-year-old kids.
Follow these links to read the other parts of this tutorial:
How To Sew An A-Line Dress