If you have the same kind that I have, it is made up of water, soap and catnip oil. Of course there are warnings on the jar that they shouldn't be injested and may irritate their eyes.
I have used them with mine and frankly they weren't all that interested enough to try to eat them. I pulled out the jar when you asked the question and am considering throwing the jar away as it isn't that satisfying of a toy for them. Besides, they leave little soap rings when they pop that you have to clean up when done.
Try it out - I can' see how it will do harm, and please tell if they like them more than mine did.