Whenever my son sees her big sisters playing "dress-up", he wants to play too. I know some boys do that too. My son doesn't even mind putting girl's dress up clothes when he wants to play "dress up". However, I do. I have to sew something for him to play too. So, I took him to a fabric store, he picked the "Star War" one himself. This particular fabric gave me an idea, ---- a cape.
1. Measure the child from base of neck to the length you want it to be, and plus 3 1/2 inch for bottom and top hem. Use the whole width. (usually 45" wide)
2. Iron the bottom hem. Fold in 1/4 inch first and then 1 inch again. Sew the double fold hem.
3. Sew double hem at sides. Fold at salvage edge and fold it again to form double hem. Sew.
4. Sew the other side of the side seam the same way. Fold in the pressed bottom hem first and then the double folded side seam
5. Press/iron the top hem. Fold in 1/4 inch first and then 3/4 inch again.
6. Sew on pressed edge to form a casing.
7. Use a safety pin, bobbin pin, or bodkin which is an "elastic puller" (used in picture) to pull your ribbon or elastic through. I found a black plushy lingerie elastic, so I just used it.
8. After you pull the elastic or ribbon through, stretch the whole top to make the gather even. Try it on the child to see if the gathering is too tight or too loose. Make adjustment.
9. After adjusting the gathering sew elastic or ribbon down through all layers at side stitch line. Not the very end of opening.
Viola, all done. a cape for a boy.