One more thought for you all before I leave these shorts behind and work on something else.
Whenever I make shorts, pants, skirts, skorts, etc. I always make a little tag for the item. The tag is a way for the child to know the back of the garment from the front, as well as to remind me of the size of the garment. You see I always think I am going to remember this stuff....but I don't. I hardly remember what I had for breakfast today!
To make the tag I use a piece of cotton twill tape that I fold in half with raw edges even. Then I slip the raw edges into the casing before I stitch it.
To put the size on the twill tape you can use your sewing machine if it has a basic alphabet option. My machine does have one that I use at times. (Make sure to use a contrasting thread color on the twill tape.) At other times when I am in a hurry, I just use a fine-tip permanent marker to write the size on. Either way works and I do this with all the garments I make.