I suggest you call it Room Parents or Volunteers so you don't leave anyone out. We had some people say that they didn't think they could volunteer since they weren't parents. We quickly let everyone know that we accept anyone as a volunteer. You also might check with your district to see if there is anything the volunteers need to fill out or do. We just found out this year that all volunteers that will have contact with the children submit to a TB skin test.
Our class moms are available to the teachers to organize 4 class parties a year. They also organize any chaperones for field trips. We utilize them for our phone chain as well, and to collect emergency forms and membership money at the beginning of the year. Every May we solicit our membership to volunteer for the following Sept and get our list of interested parents from that group.