Of my three girls, my middle daughter (age 12) is the fashion girl.
She wanted this shirt (short sleeve version in white)...BAD!
It was because of the sleeves.
I've seen these sleeves on clothing in Target for both little girls and not so little girls.
They are fairly easily to replicate.
If you want to ruche the sleeves on one of your favorite patterns here is what you do.
Cut the cap of your sleeve pattern about 5 inches higher than normal.
This shows the ruched piece with a regular inset sleeve piece on top so you can compare how they look. The ruched pattern piece will also be gathered into the armhole, whereas the regular sleeve could just be eased in for a flat appearance.
Using 1/4" (or 1/8") elastic sewn into the sleeve on the wrong side of the fabric is what gives it the ruching.
On this pattern I used a 10 1/2" piece of elastic for the sleeve portion which measured 17" from cap to hem. That's about 65% of the length. So if you have your own pattern that you are adapting just keep that in mind. You could definitely ruche it up more and then just cut your elastic a little shorter still.
Line up the elastic about 1/2" from the cap of the sleeve down to about 1" shy of the hem.
I just sewed a straight stitch right down the middle of the elastic.
It can be a little awkward stretching the elastic to fit into the sleeve. Use as many pins as you need to hold it in place. And really, if it isn't a perfectly straight line it shouldn't show. It'll all be ruched up in the sleeve.
Some other changes just on the shirt itself:
We cut the front neckline slightly lower--maybe 1 inch, AND adjusted the shoulder seam so that it was not so boatneck style. Extended the shoulder seam about 1 inch also.
'Cuz the fashion girl is particular about those things.
You can see my lines in blue showing where to cut and how I altered the pattern (size small).
Don't forget to extend the shoulders on both the front and back pieces. Or you'll be really unhappy and end up cutting out another back piece.
I'm also loving the long sleeve green version with the draping/shawl collar.
Daughter #1 is partial to that one too, in green.
I hope to show that one sometime soon, too.