But how you talk to parents and potential volunteers about that struggle can make all the difference in whether you can overcome or whether you'll be stuck in volunteer limbo for the long term.
The temptation when things are especially frustrating is to whine to parents or try to "guilt" them into trudging down to school to help out. It's basically a version of "the same five people (us) can't do everything; everyone should be pitching in!" Of course that whine is true, but it's not effective.
You might get a few volunteers who react to the guilt trip, but not many and not for the long term. If you want to attract volunteers, you need to be attractive (appear as fun, appear as welcoming, appear as worthwhile). And guilt and whininess are the opposite. Making your group more attractive and communicating positively -- even when things are most frustrating -- is the key to change. It won't work overnight, but it always works better than the negative approach.
We have a ton online about the "guilt trap" and attracting volunteers; here are just a few:
Escaping the Guilt Trap
Confront the Fear of Quitting
9 Steps To Recruit More Volunteers