Informed by the biological sensitivity to the context (BSC) theory, this multimethod, longitudinal study sought to examine how family context may be associated with the development of child sensory processing sensitivity (SPS) over a year. Participants were 235 young children (M[subscript age] = 2.97 at the first measurement occasion, 55.3% were girls) and their parents (median annual household income: $55,000 to 74,999), who were followed for two annual measurement occasions. These children consisted of 56.2% White, 21.3% African American, and 16.2% mixed race. Child SPS was measured via behavioral observation within multiple laboratory tasks at both waves and exhibited moderate stability over time. A curvilinear association between environmental harshness and the change in child SPS emerged, which proved consistent with the U-shaped pattern hypothesized by the BSC theory. Children remain at similar levels of SPS over the year under low and high levels of environmental harshness but exhibited decreases in SPS under moderate levels of environmental harshness. A follow-up exploration for the developmental implication of SPS change showed that children with higher SPS benefited more from the supportive environment by developing greater cognitive and behavioral functioning.