Early childhood development literature has emphasized the role that parental investment and early life conditions play on human capital formation. Still, there is little evidence on the mechanisms driving such dependence. This dissertation examines potential mechanisms explaining the relationship between parental investments, early life conditions and children’s outcomes. The first chapter exploits a plausibly exogenous variation on the timing at which a maternity leave extension reform was implemented to estimate the causal effect of additional weeks of maternity leave on breastfeeding duration in Chile. By using data from the Chilean Longitudinal Survey of Early Childhood (ELPI), I find that additional weeks of maternity leave increases significantly breastfeeding duration; however, the effects show substantial heterogeneity by socioeconomic status in favor of low-educated mothers, suggesting that the reform has equalizing effects. The second chapter examines how parental investments respond to differences in the initial endowment between siblings within families, and how parental preference tradeoffs vary between families with different maternal education. Using ELPI twins data, I find that preferences are not at the extreme of pure compensatory investments to offset endowment inequalities among siblings nor at the extreme of pure reinforcement favoring the better-endowed child with no concern about inequality, but that parental investment preferences are neutral, so that they do not change the inequality on endowment differentials, a result that is consistent across families with low- and high-educated mothers. The third chapter provides empirical evidence on the effects of birth weight on cognitive and non-cognitive development. Results from singletons births show a positive association. The first-difference models for identical twins, show that birth weight does not have a significant effect on the developmental test scores. However, twins estimates stratified by age of the children show that birth weight effects are positive and significant but only for children between 3 and 7 years old. Overall, I conclude that endowments at birth, parental investments and policy interventions are all key determinants to unravel children’s outcomes, and exploring the role that age and socioeconomic heterogeneity play in the production of these outcomes seems to be key for a thorough understanding of early childhood inequalities.