Double prong barrettes/metal slips, size depending on age of the wearer
3/8" grosgrain ribbon
Hot glue gun and glue
Flower, gem, button, etc. for decoration

First, cover your metal clip/barrette with the ribbon to hide the clip itself. Take the end of the ribbon, open the clip and slide the ribbon to the inside as close to the spring as possible. Come around to the open end and then on the top-side of the clip. Keep going to the end that you push down on to open and then go under the edge and cut. Quickly hot glue this piece on the clip and push down everywhere firmly till it holds. If it doesn't hold the first time, remove it and the glue and start again. Set it aside.

Make a simple bow from the same grosgrain by figuring out how long your clip is, double that and add a little extra length to hang over a little bit on each side. Cut. Fold to make a long loop and hot glue the 2 ends together. Then position the glued side down in the middle and sew a few stitches in the middle to make it look like a bow or hot glue it. I prefer to sew a few stitches, especially since the next step also includes hot glue, which might make it a little bulky.

Choose your decoration for the middle, a button, a flower or a gemstone and attach with hot glue or sew it on directly in the middle.