The Canadian Society for Exercise Physiology (CSEP), with assistance from multiple partners, stakeholders, and researchers, developed the first Canadian Sedentary Behaviour Guidelines for the Early Years (aged 0–4 years). These national guidelines are in response to a call from health and health care professionals, child care providers, and fitness practitioners for guidance on sedentary behaviour in the early years. The guideline development process followed the Appraisal of Guidelines for Research Evaluation (AGREE) II framework. The recommendations are informed by evidence from a systematic review that examined the relationships between sedentary behaviour (predominantly screen time) and health indicators (healthy body weight, bone and skeletal health, motor skill development, psychosocial health, cognitive development, and cardio-metabolic disease risk factors) for three age groups (infants aged <1 year; toddlers aged 1–2 years; preschoolers aged 3–4 years). Evidence from the review was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. The new guidelines include a preamble to provide context, followed by the specific recommendations. The final guidelines benefitted from extensive on-line consultations with input from >900 domestic and international stakeholders, end-users, and key informants. The final guidelines state: for healthy growth and development, caregivers should minimize the time infants (aged <1 year), toddlers (aged 1–2 years), and preschoolers (aged 3–4 years) spend being sedentary during waking hours. This includes prolonged sitting or being restrained (e.g., stroller, high chair) for more than 1 h at a time. For those under 2 years, screen time (e.g., TV, computer, electronic games) is not recommended. For children 2–4 years, screen time should be limited to under 1 h per day; less is better.