I tried couple of different key holders with fabrics. I got some magnetic buttons and key rings from shops.
You might have already guessed how I made them, but if you'd like to see some detail, these photos on how I made a very similar name tag accessory to attach to school bag can shed some lights. This is a name tag for a car loving boy.
First, I drew a pattern just the way I want...
Wheels are made separately..
Close the window with blind stitches and do decorating stitches including the name for the owner.
Connect the sides of front and back with blind stitches.
Attach a rubber string. If you tie a key ring at one end, you can use it a key holder.