Cow's milk is a dietary staple for children in North America. Though clinical guidelines suggest children transition from whole (3.25% fat) milk to reduced (1%) fat milk at age 2 years, recent epidemiological evidence supports a link between whole milk consumption and lower adiposity in children. The purpose of this trial is to determine which milk fat recommendation minimizes excess adiposity and optimizes child nutrition and development. CoMFORT will be a parallel group randomized controlled trial among children aged 2 to 4 years participating in the TARGet Kids! practice-based research network. Children will be randomized to receive one of two usual care nutritional recommendations: 1) a recommendation to consume whole milk, or 2) a recommendation to consume reduced (1%) fat milk. The primary outcome is Body Mass Index z-score (zBMI); secondary outcomes will be cognitive development (using the Ages and Stages Questionnaire), vitamin D stores (serum 25-hydroxyvitamin D), cardiometabolic health (glucose, hsCRP, non-HDL, LDL, triglyceride, HDL and total cholesterol, insulin, and diastolic and systolic blood pressure) and sugar sweetened beverage intake (measured by 24-hour dietary recall). Outcomes will be measured 24 months post-randomization and compared using ANCOVA, adjusting for baseline measures. This trial will contribute to nutrition policy for children in effort to reduce childhood obesity using a simple, inexpensive and scalable cow's milk fat intervention.