The boy's name is Isaiah, and his nickname is Eyeball, so I made an eye with an 'I' in the center for his super hero symbol.
Start with a piece of fabric, cut to desired length measured against child's back, stopping a few inches from the floor, for ease of movement.
attach a pony tail holder to one corner of the top of the cape, and a large button or bead to the other corner, to make a toggle clasp.
on a piece of scrap fabric, draw and paint a symbol for your child's super hero name. Allow to dry, then glue to middle-back area of the cape.