Background: As children now spend increasing amounts of time in out-of-home care, care providers play an important role in promoting positive health behaviors. Little is currently known about providers' perceptions and beliefs about physical activity, particularly for very young children. This study describes providers' perceptions and beliefs about infants' and toddlers' physical activity, and assesses their knowledge of physical activity guidelines, to establish if and where providers may need support to promote physical activity in child care settings. Methods: We analyzed baseline data from a pilot randomized-controlled trial conducted in 32 child care centers in Massachusetts, USA. Providers completed physical activity-related questionnaires from which we compared twenty perception and belief questions for infant and toddler care providers. Results: 203 care providers (96% female, mean +/- SD age: 32.7 +/- 11.2 years) from 29 centers completed questionnaires. A large proportion of providers (n = 114 (61.9%)) believed that infants should be active for 45 minutes or less each day, and only 56 providers (29.7%) perceived toddlers to require more than 90 minutes of activity per day. 97% of providers perceived it was their job to ensure children engaged in a healthy amount of physical activity and most (94.1%) perceived physical activity to be important to own their health, despite 13.3% finding it hard to find the energy to be physically active. Conclusions: This study is the first to assess the physical activity perceptions and attitudes of providers caring for infants and toddlers. Though all providers believed toddlers should engage in more physical activity than infants, most providers believed that young children require only a short amount of physical activity each day, below recommended guidelines. How provider perceptions influence children's physical activity behavior requires investigation. (author abstract)