Parents vary substantially in the frequency and complexity of the math support that they provide to their children, and this variability is often related to their children's math knowledge. We hypothesized that parents' knowledge about the development of two critical early math topics would help explain some of this variability in their early math support. U.S. parents of 3- and 4-year-olds (N = 196 mothers and 148 fathers, 94% identified as the child's primary caregiver and 77% as White; 79% had at least a bachelor's degree) reported on their knowledge about the development of early numeracy and repeating patterning skills, numeracy and repeating patterning beliefs related to their children, numeracy and repeating patterning support, and education, income, and employment status via a survey. Parents’ knowledge about early repeating patterning development was positively related to all the measured child-specific repeating patterning beliefs and both were predictive of the frequency and complexity of their reported repeating patterning support. Their knowledge about early numeracy development was also positively related to most of their child-specific numeracy beliefs, but while their child-specific numeracy beliefs uniquely predicted their reported numeracy support, their knowledge did not. Parents’ knowledge about early numeracy and repeating patterning development was not consistently related to their education, income, nor employment status, but their education and employment status uniquely predicted their numeracy and repeating patterning support. Implications of these findings for research, theory, and parent-based interventions are discussed.