Recent evidence suggests that infants can generate expectations about future events from a sample of probabilistic data. However, little is known about the conditions that support the development of this ability. Three experiments tested the prediction that 8- and 12-month-olds respond to base rates as well as perceptual cues when they generate expectations from a sample of probabilistic data. Results revealed that 12-month-olds were sensitive to the statistical and perceptual properties of the evidence depending on the distribution of high-to-low base rate items in the sample. Specifically, 12-month-olds focused on perceptual features of the evidence when a sample was large and more skewed (e.g., 6:1), whereas they attended to statistical properties when the sample was smaller and less skewed (e.g., 4:1). In contrast, eight-month-olds always focused on the perceptual features of the evidence. Neither group generated expectations from a small, less skewed sample (e.g., 2:1). These results suggest that the ability to generate expectations about future events is mediated by specific features of the available evidence and undergoes significant change during the first year of life.