A growing body of research suggests that parents' beliefs about and attitudes toward math predict their young children's math skills. However, limited research has examined these factors in conjunction with one another or explored potential mechanisms underlying these associations. In a sample of 114 preschool-aged children and their parents, we examined how parents' beliefs about math and math anxiety together relate to children's math achievement and how parents' practices to support math might explain these associations. We used a range of measures of parental math input, including survey measures of the home numeracy environment as well as observations of number talk. Parents with stronger beliefs about the importance of math tended to have children with more advanced math skills, and parents with math anxiety tended to exacerbate the effects of these beliefs such that children whose math-anxious parents held strong beliefs about math's importance performed best. Furthermore, we found some evidence that parents' math practices may relate to this interaction or to children's math skills, but no single measure of math input mediated the effect of the interaction between parental math anxiety and parental math beliefs on children's math outcomes. Thus, parents' math anxiety differentially relates to children's math performance depending on parents' beliefs about math, but future research is needed to uncover the specific mechanisms through which these processes operate.