Background:
     
     In South Asia, 89 million children under 5 are at risk of not reaching their developmental potential. Household socioeconomic position (SEP) is a determinant of early child development (ECD). However, synthesised evidence for the association between ECD and SEP in young children in South Asia is not available. Therefore, this review synthesises evidence on the relationship of household SEP with ECD in children under 36 months of age in South Asia.
   

Method:
     
     PubMed, Cochrane Library, MEDLINE and Scopus were systematically searched to identify studies from South Asian countries that reported evidence on the association between SEP and ECD. Search terms included items related to motor, cognitive, language and socioemotional development. Study quality was assessed using the QualSyst tool, with three quality levels (high/medium/low), and a narrative review for each ECD outcome was constructed (PROSPERO registration: CRD42019131533).
   

Results:
     
     Twelve of the 950 publications screened met the inclusion criteria (nine from India, two Nepal and one Bangladesh). The majority (n = 10, 83%) reported language development on its own or alongside another ECD outcome. Fewer articles assessed cognitive (n = 6, 50%), motor (n = 7, 58%) or socioemotional development (n = 3, 25%). Higher SEP was associated with better ECD for one third of the associations reported. One ECD outcome (socioemotional development) was negatively associated (with socioeconomic status) based on low quality evidence. Mother's education and family income were the major SEP constructs associated with ECD. One, four and seven studies were rated as having a low, medium and high risk of bias, respectively.
   

Conclusion:
     
     This review reveals the scarcity of evidence exploring associations between household SEP and ECD in children under 36 months in South Asia, especially outside of India. Enhancing evidence for associations between ECD and SEP is needed for evidence-based policy making to reduce developmental delays associated with a disadvantaged SEP in the South Asian region.