It is a common practice among heirloom patterns, or patterns in general, when stitching the sleeves seams in a bishop, stitch the sleeve seams then pleat the bishop. Next to stitch the side seams you run the stitching down the side seam from the bottom edge of the sleeve all the way down the side of the dress to the bottom of the dress hem. I'm not a fan. I don't want lumps and bumps in my armpits when my arm is hanging at my side and I don't imagine children do either. Especially if you have a child with sensory issues. They are going to squirm and wiggle with those seams bunching under their armpits. It is possible to have a set in the round sleeve on a bishop. I am in the process of pre-constructing a bishop for our baby and decided to share this finishing method with you, faithful reader.
The first thing you have to do when stitching your sleeve seams is to stop about an inch or two before the end of the seam.The x's mark where I stopped stitching. I had done seamless pleating on this bishop, so my seams are unfinished at this time. We'll get to that later.
I French seamed the sleeve and the sides of the dress. Yes, it is a bit fiddly, but it is worth in my opinion. Then I finished the sleeve hem with a narrow hem. You can see I haven't taken my "cheater stitching" out yet where I marked my 1/4" hem allowance. But I have a clean finish to the bottom of my sleeve without that "thing" peeking out at the bottom of the sleeve.
Here is the resulting "hole" in the sleeve seam after the French seams are done.
I pin the remaining underarm seam together matching my French seams.
I hope you can see this, the sun was shining in the window right at my presser foot. I just stitch the remaining seam, making sure to match my stitching lines from constructing the upper sleeve seams.
Voila! My sleeve in set in in the round with no lumpy fold over business under the arm. Now to finish that seam edge.
You can trim and then zig-zag the edge, you can use seam tape to finish, you can serge the seam allowance or you can use a mock rolled hem, which is what I have done.
First trim one side of the seam allowance to 1/8". The remaining seam allowance is 1/4".
I press the wider seam allowance over the shorter one with my iron. Now we are ready to do the mock rolled hem. It is also called a faux French seam, Cindy Foose calls it a toymaker stitch. Doesn't matter what you call it, it is very easy to achieve. Along the seam on the short side, starting at the right if you are right handed, I take a stitch right next to my stitched seam. Then travel to the fold of the pressed edge of the larger seam allowance and again take a stitch. Alternate back and forth between the stitched seam and the folded edge for a couple of inches.
Then pull your working thread until the folded edge curls over to meet the seam stitching on the shorter side.
Pull until if looks like this. I have used waxed thread I purchased from Wendy Schoen. It is a Sarah Howard Stone product. Inquire at your favorite heirloom shop. Regular weight sewing thread that you wax yourself works just as well. But you really need a waxed working thread to prevent breaking when you tug to form the roll. Continue in the same way, stitching your alternating stitches for a couple inches, pull to roll, until you reach the other side. It does not take that long, I timed it, 20 minutes to do this seam.
Here is my finished faux French seam. Tiny, neat and trim. Now to apply the bias band, then I can get to smocking little punkins and leaves.