If VBS is God's work, you can count on Him to provide the needed help. Rather than a general call from the pulpit (“anyone interested in working in VBS see so-and-so after church“), directly contact people. Sixty percent of people in any congregation do NOT respond to general announcements! One-on-one recruitment is always the most effective, and also eliminates the possibility of individuals responding for a position who are not qualified. Ask specific people for a specific job.
Running an effective Vacation Bible School requires an excited, dedicated and coordinated staff. Have in hand a list of all needed positions, such as: advertising, Bible discovery, nursery child care, class coordinator, crafts, decorating, games, mission project, music, photography, preschool, puppetry, registration, set-up/dismantling crew, supplies shopper, snacks, teacher assistants, transportation, etc.