Start with your pillowcase and measure the length from just under the top of your child's under arm-about 3 inches down from it- to her mid hip bone (my daughter is 6 yrs old and her's was 13 inches) add 1/2 inch for hem.
Cut across top of pillowcase from one side to the other (make sure you are measuring length vertically and horizontally on each side and marking it to assure straight lines)
Now find another fabric (design fabric) that you feel compliments your pillowcase fabric cause this will be the Top part of your shirt. I made this fabric 6 1/2 inches wide (vertically) and 31 inches length wise (horizontally) and cut that fabric. Fold it over nice side facing out and iron to hold fold in place.
Take your pillowcase fabric and start to make pleats in the front and back (ironing and pinning down to top of fabric pleat to assure hold) Make just enough pleats to fit your design fabric in when wrapped around bottom of shirt ( I made 3 pleats in the back and 4 in the front about 1/2 inche wide)
Sew over pleats to hold them in place.
Take your pillowcase (inside out) and your design fabric and line design fabric (front side out) starting from the back of the pillow case. Use the open side of your design fabric to start in the back of pillowcase shirt and sew together
This is how it should look when you flip the pillow case right side out. Now fold your designer fabric in half (open side-in) leaving 1/2 inch length hanging over the top of pillow case seam- and iron to assure hold- pin it in place and sew.
For the Straps:Measure the length from front to back of your child's shoulders (or however long you want your straps to be) I did 14 inches long and 3 1/2 inches wide, measure and mark them in 3 parts width wise Mark and fold outsides in. Iron and sew.
I Don't have a picture but I sewed some elastic about 4 inches long in the back of the shirt on the the top of the designer fabric to add a better fit and look to the shirt (Sew the elastic in the middle center of designer fabric just between where your straps will be)
For placement of straps I took the shirt and measured where I wanted the straps to be, on my daughter and then pinned them to the shirt and careful removed the shirt (you can always use some tailors chalk but I didn't have any) lol be careful : )
If you wish to hide your straps, you can always place them behind the designer fabric- Pin, and sew in place (however, I chose to show the front straps, tuck them under and sew them in place) because i thought it added more character to the shirt : )
And your done : )
P.S. You can always add buttons, a fabric flower, whatever you like, Make it your own and Most of all
Have Fun and Be Creative <3