Since then, I have made several others, since he sometimes loses them, or I put his pants in the washer and forget to search the pockets. The last one was orange and apparently it was misplaced sometime last Saturday (I'm decluttering, so I may have some responsibility in the matter, though I honestly don't remember picking it up), so I made a new one and this time I took some pictures to make a mini tutorial.
What you need: a strip of felt (scraps are welcome), matching thread and a cute boy button.
Fold the felt as shown, to create a pocket with a flap...
...and then sew the sides:
I hand stitched the sides using a blanket stitch, but any other stitch is OK. Machine sewing also works, though you may not want to re-thread your machine for such a small project.
Sew the button...
...and then cut a small slit on the flap, just long enough for the button to pass through. Since felt doesn't fray, making button casings is as simple as this.
Your coin purse is ready!
You can obviously also make a girly version of the coin purse, but in my experience girls want bigger purses. My daughter usually requests to have her own version of everything I make for her brother and this time she was totally uninterested, so it may be a good indication...