ABSTRACT: BACKGROUND:In early life, both mothers and fathers are important influences on their children's diet, active play, and obesity risk. Parents are increasingly relying on the internet and social media as a source of information on all aspects of parenting. However, little is known about the use of Web-based sources of information relevant to family lifestyle behaviors and, in particular, differences between mothers' and fathers' use and sociodemographic predictors. OBJECTIVE:The objective of this study was to examine if mothers and fathers differ in their use of the internet for information on their own health and their child's health, feeding, and playing and to examine sociodemographic predictors of the use of the internet for information on these topics. METHODS:We conducted a secondary analysis on data collected from mothers (n=297) and fathers (n=207) participating in the extended Infant Feeding, Activity and Nutrition Trial (InFANT Extend) when their children were 36 months of age. The main outcome variables were the use of the internet for information gathering for parents' own health and child health, feeding, and playing. Binary logistic regression was used to examine the sociodemographic predictors of outcomes. RESULTS:Compared with fathers (n=296), a higher proportion of mothers (n=198) used the internet for information on their own health (230, 78.5% vs 93, 46.5%), child health (226, 77.1% vs 84, 42.4%), child feeding (136, 46.3% vs 35, 17.5%), and child play (123, 42.1% vs 28, 14.0%) and intended to use Facebook to connect with other parents (200, 74.9% vs 43, 30.5%). Despite the high use of the internet to support family health behaviors, only 15.9% (47/296) of mothers reported consulting health practitioners for advice and help for their own or their child's weight, diet, or physical activity. Sociodemographic predictors of internet use differed between mothers and fathers and explained only a small proportion of the variance in internet use to support healthy family lifestyle behaviors. CONCLUSIONS:Our findings support the use of the internet and Facebook as an important potential avenue for reaching mothers with information relevant to their own health, child health, child diet, and active play. However, further research is required to understand the best avenues for engaging fathers with information on healthy family lifestyle behaviors to support this important role in their child's life. TRIAL REGISTRATION:ISRCTN Registry ISRCTN81847050; http://www.isrctn.com/ISRCTN81847050.