# **1 Introduction**

Investments in early childhood are a critical determinant of later life outcomes, and stimulating activities — for example, shared reading and infant-directed speech — are an important way that older family members invest in young children (Knudsen, Heckman, Cameron, and Shonkoff 2006, Grantham-McGregor _et al_ . 2007, Almond and Currie 2011, Walker _et al_ . 2011, Aizer and Cunha 2012). Underinvestment in early childhood is an acute problem in low- and middle-income countries (LMICs), where an estimated 43 percent of children are at risk of failing to meet their developmental potential because of inadequate nutrition and cognitive stimulation (Black _et al_ . 2017). A growing interdisciplinary literature examines the causes and consequences of parental investments in young children in LMICs, seeking to identify interventions that can change parenting practices to improve developmental outcomes in children and increase incomes in adulthood (cf. Gertler _et al_ . 2014, Black _et al_ . 2017, Andrew _et al_ . 2018). However, parents are not the only caregivers in most societies — in many low-income contexts, much of that work is done by older siblings, particularly sisters (Weisner _et al_ . 1977, Lancy 2015). Though this pattern is well-documented in the anthropology literature, older siblings’ role in childrearing is often ignored in academic and policy discussions of investments in early childhood.<sup>1</sup> We model older siblings’ contributions to the human capital accumulation of young chil-

> 1Though older siblings are known to play an important role in caring for young children in LMIC contexts, standard approaches to quantitative measurement frequently ignore both the investments older children make in their younger siblings and the impacts that early childhood interventions (including those that seek to change childrearing practices) might have on sibling caregivers. For example, the standard format of the Family Care Indicators, one of the most widely used measures of early childhood stimulation, does not record stimulating activities carried out by household members under 15 years old (Hamadani _et al_ . 2010, Kariger _et al_ . 2012). Researchers also tend to ignore the potential impacts of parenting interventions on sibling caregivers. For example, a recent systematic review of 466 impact evaluations of early childhood development interventions in LMICs found that only four measured indirect effects on older siblings in middle childhood or adolescence (Evans, Knauer, and Jakiela 2020). This tendency to ignore the caretaking role of older siblings is at least partially attributable to the widespread perception that parental stimulation is more beneficial to young children than stimulation by older children (though it may also entail a higher opportunity cost). In a published response to Weisner _et al_ . (1977), Brian Sutton-Smith argued that “Maximal personal and social development of infants is produced by the mother (or caretaker) who interacts with them in a variety of stimulating and playful ways. Unfortunately the intelligence to do this with ever more exciting contingencies is simply not present in child caretakers,” Weisner _et al_ . (1977, p. 184). Thus, sibling caregiving, though widespread, is often considered a second-best alternative to greater maternal investment — particularly since childcare responsibilities might limit older siblings’ ability to invest in their own human capital through formal schooling.

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