Randomisation and blinding: Families will be randomized at a 1:1 ratio to either intervention or control group, stratified by sex using a central computerised system. Participants will be aware of their group allocation, but all assessors will be blinded to treatment allocation. Justification of sample size: Based on our previous research with exergames, 80 families (40 per group) will be recruited to detect a medium effect size (f2 = .25; (38)) in adherence to physical activity (primary outcome) with a type one error of .05, an average correlation of .75 across time for our DV of interest, and a power of .80. Our sample size also considers the main 2 (group) x 2 (parent/child) x 4 (time) repeated measures design using G-Power and a potential 15% attrition rate.