Disclaimer: This really isn't a tutorial and can probably be filed under 'Well, duh' but I'm sharing it anyway because sometimes the 'Well, duh's pass us by. Or at least they pass me by.
Due in part to me failing to make my own kids any clothes in forever, Maia has very few long sleeve tops that fit her now that the weather has grown cold. Like most kids, she has grown far more vertically than horizontally (she has actually lost most of her toddler shape) in the last year so tops fit her in the body but come up short. But with a bit of ribbing and less than an hour, half a dozen tops have been given an extra year of wear. Remember this one?
Let's give it another year.
A top that has normal hems (i.e. does not have cuffs already)
Ribbing (or jersey works too provided it's not too flimsy). You could also upcycle the ribbing from other out grown garments.
Cut a piece of ribbing that is roughly 5.5" to 6" high and half an inch narrower than your sleeve hem when the ribbing is folded. Do this for both sleeves.
Cut two pieces of ribbing that are roughly 5.5" to 6" high and an inch (or a bit more if your ribbing is super stretchy) narrower than your hem.
Cut the sleeve hems off at the stitch line.
Same for the hem.
On the opposite side from the fold, sew the raw edge of a sleeve cuff together. Take a picture upside down to prove it. Repeat for other sleeve cuff. Then repeat to both sides of the hem ribbing.
Fold it down so the stitching is to the inside. Same for other sleeve cuff and hem ribbing.
With the sleeve right side out, place the cuff over the top of the sleeve edge so that all three edges are aligned. Stretch the ribbing to fit and pin in place.
Sew along the raw edge all the way around, stretching only the ribbing to fit. Repeat for other sleeve.
With the shirt still right side out, place the hem ribbing around the bottom edge so that all three raw edges align. Match the side seam of the shirt with the side seam of the hem ribbing and pin in place. Repeat on opposite side. Stretch the ribbing to match the shirt's edge and pin all the way around.
Sew along the raw edge all the way around, stretching only the ribbing to fit.
Flip down all of the cuffs and you're done. An extra two and half inches to the sleeve and hem and another year of wear.