Recent work provides evidence that expectations regarding a fair (i.e., equal) distribution of goods and resources arise sometime in the second year of life. To investigate the developmental trajectory of fairness expectations, and their potential relation to prosocial behavior, infants participated in a violation-of-expectancy (VOE) paradigm designed to assess expectations regarding how resources are typically distributed, and in a sharing task, an informational helping task, and an instrumental helping task. Infants’ expectations regarding resource distribution showed age-related changes between 12 and 15 months, with only 15-month-old infants showing greater attention to unfair (unequal) over fair (equal) outcomes in the VOE. Individual differences in infants’ sensitivity to unfair outcomes were related to infants’ willingness to share a preferred toy. In contrast, helping behavior was unrelated to infants’ sensitivity to unfair outcomes and did not vary according to whether infants shared a preferred or non-preferred toy during the sharing task. Our findings suggest a developmental transition in expectations regarding how resources are distributed from 12 to 15 months of age, linked to infants’ sharing behavior, suggesting that such expectations are learned through experience. Our results also contribute to the ongoing discussion regarding how best to assess the construct of prosociality in infancy.