Sewing Machine and supplies
You can also do this with newborn size and other types of clothes, but for the tutorial lets stick with a premie size onsie. Look how big it is compared to the doll. Way too long.
3) Fold the end over two times and Iron it down.
Below is another shirt I did. It isn't a onsie and it is size newborn so it was a little bit different but I wanted to show that you really can do it to most baby clothes.
All I did was put the shirt on the doll inside out. Then I pinned it down the front and sides and sewed it smaller. I also shorted the hem like I did for the onsie. This shirt has buttons on the back and is still a little tight to put on the doll, so make sure you have enough room in the neck to get the arms in and out.
I also made an adorable newborn sized swimsuit and a few other things this way. I spent one nap time on it and about $5 and got a few different outfits for my girls to play around with. A great investment!