It can be pretty tricky sewing cuffs onto leg or sleeve edges, particularly with childrenswear when the pieces are so small. Added to that, as the ratio of cuff circumference to garment circumference increases, the difficulty increases too. For example, a leg cuff on my newborn trousers is 15cm but the leg hole I'm attaching it to is 23cm; that's a lot of stretching to match, and not a lot of space to do it in!
Before I sew a cuff on, I pin the cuff to the leg opening only at the four quarter marks and stretch to match the bits in between as I sew. I'm doing this on my serger, but the same applies on a regular sewing machine. And here's how I do it:
As the video is pretty fast and I don't do any talking, here's the bits that I think are most helpful:
Sewing on the curve:
Don't attempt to stretch the entire band to match the garment edge, it's much easier to stretch just the edge of the band as it has a cut edge that will naturally fan out. And by leaving the bulk of the band unstretched, you are maintaining its intended circumference rather than stretching it out of shape. And so you end up with a nice neat circle at the end:
Folding up to check edge alignment:
I tend to pause every couple of inches, and with the needle in the down position fold up to make sure all the edges are flush and to tame any of the curls. Once I'm happy, it's folded back down onto the plate, squashed down with various fingers and sewn again on the curve.
And there you go, a nice and neat cuff in no time at all.