IntroductionChildren with developmental coordination disorder (DCD) are less physically active than their typically developing peers. No substantiated interventions are available to address this issue. Therefore, this study aims to describe the design and rationale of (1) a family-focused intervention to increase motivation for physical activity (PA) and, indirectly, lifestyle PA in children aged 7–12 years with DCD and (2) the methods to examine its preliminary effectiveness and feasibility.Methods and analysisThis intervention is the second part of a more comprehensive, multidisciplinary treatment called We12BFit! The intervention was developed using the steps of treatment theory which includes the concept of targets, mechanism of action and essential ingredients. The content of the intervention is based on the transtheoretical model of change (TTM). In the intervention, the motivation for PA will be targeted through application of behaviour change strategies that fit the stages of the TTM. The modes of delivery include: pedometer, poster, parent meeting, booklet and coaching. At least 19 children with DCD, aged 7–12 years, will be included from two schools for special education and two rehabilitation centres. The intervention will be evaluated using a single-arm mixed-method design. Effectiveness will be assessed at three instances by using ActiGraph accelerometers accompanied by an activity log. Feasibility will be assessed using interviews with the participants and coaches. This evaluation may add to our understanding of motivation for PA in children with DCD and may eventually improve the rehabilitation programme of children with DCD.Ethics and disseminationThe study has been approved by the Medical Ethics Committee of the University Medical Center of Groningen (METc 2015.216). We will disseminate the final results to the public through journal publications and presentations for practice providers and scientists. A final study report will also be provided to funding organisations.Protocol version4, 12 April 2018.Trial registration numberNCT6334; Pre-results.