AIM: This review aimed to summarise the evidence related to the feasibility, efficacy for increasing physical activity, and implications of smartwatch activity tracker use in preschool-aged children. METHODS: In November 2023, we searched Medline, PsycINFO, CINAHL, Web of Science, ProQuest Central and SPORTDiscus. From an initial 7449 studies, we included 15 studies that explored the use of smartwatch activity trackers in preschool children aged three to 5 years. Data were extracted on feasibility, efficacy, and reported advantages and disadvantages of use. We used the preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. RESULTS: Studies that reported adherence to wear indicate good feasibility. No studies evaluated the efficacy of activity trackers for influencing physical activity and sedentary behaviours. Potential limitations of activity tracker use by preschool children include discomfort and a loss of interest. CONCLUSION: Smartwatch activity trackers may be feasible for use by preschool children, but no studies have explored whether these devices can increase physical activity in this age group. Short-term use of these devices may encourage physical activity by promoting family discussions and increasing awareness of physical activity, but discomfort and a loss of interest over time may be barriers to long-term use by young children.