This tutorial will take you step by step through downsizing a zip collar sweatshirt from and adults to a child's. The one I'm cutting down is a size small, and I'm taking it down to a toddlers size T2. Here is the sweatshirt before cutting.
The first thing you need to do is cut the seams, you want to do the side seams, and depending on the size of the child's shirt you are making you may wish to leave the sleeves in, I've taken them out for this one as there is just room for the pattern. DO NOT cut the shoulder seams, you want to leave the shoulders and neck seams intact.
Next you want to find the centre of the sweatshirt and place your pattern pieces on it
Try and line up the shoulders, there will probably be a bit of extra length when you sew the arms in, but you can trim that off with the overlocker (or by hand if you aren't using an overlocker)
Next cut out your sleeves, don't forget to put the right sides of the fabric together so you get a left and a right sleeve.
Here is the cut down front and back, next we will be sewing the sweatshirt up.
To sew up, line the centre sleeve with the shoulder seam and sew the sleeves in
As long as the seam and centre sleeve line up it doesn't matter if the sleeve isn't perfectly matching, you can trim the excess off when sewing up the sides.
Here is the sleeve sewn in
Now sew up the sides and arms, you want to line up the underarm seams, you can trim off excess from the cuffs and hem if needed. Once you've done the side seams hem the sleeves and hems, and all finished.
The finished article