Oooh, today is a fun one. If you've never sewn flat-felled seams before, you'll be amazed at how professional they look and how strong they are. And although they do take a little more time than just serging or pinking a seam, the process is simple and you'll be a master in no time.
To begin, make sure you have page 7 of the directions open in front of you, with the above illustration showing. It's important to get your seams oriented the right way!
Take the Front pieces and pair them with the corresponding Side Front pieces, wrong sides together. Pin, aligning the markings. I like to put a pin on the Front panel as shown, to remind me to keep that side up when I'm at my machine.
At your machine, load your topstitching thread if you're using it. (You'll just keep regular all-purpose thread in your bobbin.) Be sure to test your tension, stitch length, etc. on a scrap piece of your fashion fabric, using two layers as you will when you sew your skirt pieces together. For topstitching, it's nice to lengthen your stitch a bit. I like about 3.5mm.
With the Front pieces on top, stitch both of the Front/Side Front seams using a 5/8" (15 mm) seam allowance.
Repeat this process to sew each Side Front to Side Back, each Side Back to Back, and then the center back seam to connect the Back pieces. For each seam, pay close attention to the orientation illustration and place a pin to remind you which panel should be on top while stitching. (The panel the arrow is pointing AWAY from should always be the one on top for each seam.) Your attention to detail here will be rewarded! When you're finished, the panels will all be connected as shown above, with the center front still open.
Now is the time to try on the skirt. Then you can double-check the fit and adjust if necessary - before you finish flat-felling the seams. Fold the skirt fronts on the fold line and pin. Be sure to use safety pins here! Then safety pin or baste the waistband in place and try on your skirt. If any of the cutting or seam allowances were slightly off, this could cause fitting issues and/or the waistband not to match the top of the skirt, so make adjustments if necessary.
OK, let's finish the seams. I'll walk through the steps below, and there's also a video for this technique here. Press each seam flat, with the topstitched side on top (as shown above). (If you didn't use topstitching thread, just press the seam allowances in the direction of the arrows in the illustrations.)
Trim the seam allowance on the under side to 1/4" (6 mm). You can do this with sharp scissors or a rotary cutter, whichever you're comfortable with.
Wrap the intact seam allowance around the trimmed one as shown. Press in place and pin if necessary. (Don't pin if you're using leather or another fabric that will leave pin holes.)
Topstitch near the folded edge. Your awesome flat felled seams are complete!
Tomorrow we'll make the front placket and hem the skirt...
Below is the sizing guide I use when designing patterns. Please note that these measurements refer to your child, not to any measurements on the finished pattern.