Background: Vaccine-preventable diseases pose a significant risk to children in childcare. However, few regulations exist regarding childcare staff vaccination. This study aimed to assess support for a childcare agency staff mandatory vaccination policy. Methods: Surveys were distributed to staff and parents at 23 St Louis, Mo, childcare agencies during fall 2014. Staff and parents' support for a mandatory vaccination and/or agency certification program were compared using [chi-squared] tests. Multivariate logistic regression was conducted using a 2-level nested design and controlling for gender, race, age, and income to determine predictive models for support for a mandatory staff vaccination policy and/or agency certification program. Results: Overall, 354 parents and staff participated (response rate, 32%). Most supported a mandatory staff vaccination policy (80.0%; n = 280) or agency certification program (81.2%; n = 285), and there were no differences between parents versus staff. Determinants of support for a mandatory policy included willingness to receive influenza vaccine annually, belief that vaccines are safe and effective, and support for the policy only if there were no costs. Conclusions: There is strong support for some type of childcare agency staff vaccination policy. Implementing such a policy/program should be a collaborative endeavor that addresses vaccine cost and access. (author abstract)