Background: Accurate, reliable and feasible methods of dietary intake and physical activity assessment are required to improve our understanding of the associations between energy balance-related behaviours and health. Methods: The Synchronised Nutrition and Activity Program (SNAP™) was developed to enhance recall in children by integrating new and established methods of dietary intake and physical activity recall. A list of commonly consumed foods (n = 40), drinks (n = 9) and physical activities (n = 29) was used in SNAP™. All foods and drinks were analysed by count (i.e. the number of times a particular food was selected), as a proxy indicator of dietary behaviours. All reported physical activities were assigned an intensity code [in metabolic equivalents (METs)] to determine minutes of moderate-vigorous activity (MVPA; ≥3 METs). Results: Most participants completed a whole day's recall (both dietary intake and physical activities) in less than 25 min. SNAP™ was compared against 24-h multiple pass questionnaire and accelerometry in 121 children (aged 7-15 years old). For dietary variables, the accuracy of SNAP™ (mean difference) was within ±1 count for the majority of food groups. The proportion of the sample with a between-method agreement within ±1 count ranged from 0.40 to 0.99. For MVPA, there was no substantial fixed or proportional bias, with a mean difference between methods (SNAP™ - accelerometry) of -9 min of MVPA. Qualitatively, participants have indicated that they find SNAP™ easy and fun to use. Conclusions: SNAP™ was developed to be a simple, quick and engaging method of assessing energy balance-related behaviours at a group or population level and succeeded because it can collect a whole day's recall (dietary intake and physical activities) in less than 25 min to a reasonable and acceptable degree of accuracy.