It could also depend on where you're looking and what their needs are. Some schools are filled with parent volunteers. In our elementary school there is no shortage of parents willing to step up and be at the school multiple days/week, grades k-4, and even into the middle school. But you go into the next district over and it's a different situation. I've taught at schools that we couldn't even get a sub for let alone a single parent volunteer.
Another thing to consider is not only the space for parent volunteers but if you have a college nearby you're also competing with students who are there for their practicums in both early childhood education and elementary education. In addition to that you might be competing against college students who are there as part of their regular volunteer hours through the university civic engagement program.
While you might prefer to work with children you might also see where there is additional need in your community for volunteers. I think it's fantastic that you want to contribute, but it might be time to broaden your search.
