What you need:
One adult t-shirt in any size, I used a male medium.
FREE PATTERN: Baby Shortall Pattern size 6-12 mos
sewing supplies and sewing machine
1. Lay out your t-shirt and place the neckline of the pattern on the neckline of the shirt.
*This is where you can alter the pattern for head size and shoulder width. If your baby has a big head and wide shoulders, overlap less. If your baby has a small head and small shoulders, overlap more.
10. With right sides together line up the sleeve seams at the armpit. There will be a difference in length because of the size of the neckline. Also, the white arrow is point to the corner where the side should meet the sleeve. It doesn't meet because I overlapped my neckline 2". If you overlap yours less, I left room on the patter so that you will have more room in the sides.
This is what the inseam should look like.