The increasing childhood obesity epidemic calls for appropriate measures and effective policies to be applied early in life. Large-scale socioecological frameworks providing a holistic multifactorial and cost-effective approach necessary to support obesity prevention initiatives in this age are however currently missing. To address this missing link, ToyBox-study aims to build and evaluate a cost-effective kindergarten-based, family-involved intervention scheme to prevent obesity in early childhood, which could potentially be expanded on a pan-European scale. A multidisciplinary team of researchers from 10 countries have joined forces and will work to realize this according to a systematic stepwise approach that combines the use of the PRECEDE-PROCEED model and intervention mapping protocol. ToyBox-study will conduct systematic and narrative reviews, secondary data analyses, focus group research and societal assessment to design, implement and evaluate outcome, impact, process and cost effectiveness of the intervention. This is the first time that such a holistic approach has been used on a pan-European scale to promote healthy weight and healthy energy balance-related behaviours for the prevention of early childhood obesity. The results of ToyBox-study will be disseminated among key stakeholders including researchers, policy makers, practitioners and the general population.