OBJECTIVES To identify predictors of: uptake of the childhood influenza vaccine in the 2015-2016 influenza season, parental perceptions of side-effects from the influenza vaccine and intention to vaccinate one's child for influenza in the 2016-2017 influenza season. DESIGN Cross-sectional online survey. SETTING Data were collected in England shortly after the end of the 2015-2016 immunization campaign. PARTICIPANTS 1001 parents or guardians of children aged between two and seven. MAIN OUTCOME MEASURES Self-reported uptake of the childhood influenza vaccine in the 2015-2016 influenza season, perception of side-effects from the influenza vaccine and intention to vaccinate one's child in the 2016-2017 influenza season. RESULTS Self-reported uptake of the childhood influenza vaccine was 52.8%. Factors strongly positively associated with uptake included the child having previously been vaccinated against influenza, perceiving the vaccine to be effective and perceiving the child to be susceptible to flu. Factors strongly negatively associated with uptake included perceiving the vaccine to be unsafe, to cause short-term side-effects or long-term health problems and believing that yearly vaccination may overload the immune system. Predictors of intended vaccine uptake in 2016-2017 were similar. Participants who perceived side-effects after the 2015-2016 vaccination reported being less likely to vaccinate their child next year. Side-effects were more likely to be reported in first-born children, by participants who knew another child who had side-effects, those who thought that the vaccine would interact with medication that the child was currently taking, and those who believed the vaccine causes short-term side-effects. CONCLUSIONS Perceptions about the childhood influenza vaccine show strong associations with uptake, intended uptake and perception of side-effects. Attempts to improve uptake rates from their current low levels must address these perceptions.