Anxiety severity in youth is associated with a host of negative outcomes including poor response to treatment. Thus, a better understanding of factors that contribute to anxiety severity is needed. Such factors may include parental anxiety as well as anxiety-related approach and avoidance behaviors in both children and parents. In this study, we examined automatic behavioral tendencies as a method of quantifying anxiety-related approach and avoidance behaviors in children and their parents. Clinically anxious youth (N = 19) with mixed anxiety diagnoses and their parents completed an approach-avoidance task (AAT) comprising different emotional expressions. Our results suggest that in addition to parent report of youth anxiety, both youth and parent automatic avoidance biases predict clinician-rated youth anxiety severity accounting for 62% of the variance in clinician-rated youth anxiety. These results suggest that the AAT may be a useful measure of automatic behavioral tendencies in clinically anxious youth and their parents and that these factors may be relevant to youth anxiety severity.