Background: The use of the internet to access information is rapidly increasing; however, the quality of health information provided on various online sites is questionable. We aimed to examine the underlying factors that guide parents’ decisions to use online information to manage their child’s health care, a behaviour which has not yet been explored systematically. Methods: Parents (N = 391) completed a questionnaire assessing the standard theory of planned behaviour (TPB) measures of attitude, subjective norm, perceived behavioural control (PBC), and intention as well as the underlying TPB belief-based items (i.e., behavioural, normative, and control beliefs) in addition to a measure of perceived risk and demographic variables. Two months later, consenting parents completed a follow-up telephone questionnaire which assessed the decisions they had made regarding their use of online information to manage their child’s health care during the previous 2 months. Results: We found support for the TPB constructs of attitude, subjective norm, and PBC as well as the additional construct of perceived risk in predicting parents’ intentions to use online information to manage their child’s health care, with further support found for intentions, but not PBC, in predicting parents’ behaviour. The results of the TPB belief-based analyses also revealed important information about the critical beliefs that guide parents’ decisions to engage in this child health management behaviour. Conclusions: This theory-based investigation to understand parents’ motivations and online information-seeking behaviour is key to developing recommendations and policies to guide more appropriate help-seeking actions among parents.