This article tests whether parents reinforce or compensate for child endowments. We estimate how the difference in birth weight across siblings impacts specific parental investments: breast-feeding, well-baby visits, immunizations, and preschool attendance. Our results indicate that normal-birthweight children are 5%-11% more likely to receive early childhood parental investments than their low-birth-weight siblings. Moreover, the presence of additional low-birth-weight siblings in the household increases the likelihood of investments such as well-baby visits and immunizations for normal-birth-weight children. These results suggest that parental investments in early childhood tend to reinforce endowment differences.