You only need a few things to make very cute inexpensive button bobby pins and I'm sure you know how to make them. I'm posting the project mostly because of how I trimmed the shanks off the buttons.
If you look at all my supplies, you see inexpensive craft type buttons, decorative buttons, bobby pins and adjustable rings with glue on pads which I got very inexpensively from Rings and Things, the rings are 72 for 9.00, the bobby pins are 72 for 11.28. I used Household Goop which is a similar adhesive to E-6000. I use them interchangeably for most projects. The other thing you'll see is a pair of toe nail clippers.
I have a craft dedicated pair of toe nail clippers because they work really well for trimming small pieces of plastic like shanks on buttons and have a built in file for smoothing and texturing surfaces. It's a trick I hit on while my son and I were discussing the best way to trim sprues from his plastic models and miniatures.
That's one untrimmed button and one that's trimmed so you can see them a little better.
So after you get the decorative buttons trimmed, you just glue them to a plain button then glue that to the pad on the bobby pin or adjustable ring. Superglue will also work very well to connect plastics but my Superglue was super gunky. For younger kids, you'll want to do all the gluing because both glues have fumes.
My daughter and I are planning to do a table at least one of the local fairs this year so I've been looking for inexpensive things we can make to sell. We will package the bobby pins in sets of two on business cards.
If you're making bobby pins and they have a direction like my bats, make sure you make them opposites or you'll have two pretty button bobbies for the same side!
I also gave some of the ring blanks to my son, who will probably wind up making little toy gun rings using some of the weapons from his old toys and things like that. I told the kids if they like the adjustable rings well enough and they sell well, I'll also make them some sterling adjustable rings to decorate.