IntroductionEarly childhood interventions primarily focus on the mother–child relationship, but grandmothers are often critical in childcare in low-resource settings. Prior research is mixed on how grandmother involvement influences child outcomes and there is a paucity of research on grandmother caregiving in low-income and middle-income countries. We examined the role of grandmother involvement on child growth and development in the first 2 years of life cross sectionally and longitudinally in rural Pakistan.MethodsWe used data from the Bachpan Cohort, a longitudinal birth cohort in rural Pakistan. Maternally reported grandmother involvement in daily instrumental and non-instrumental caregiving was collected at 3 and 12 months. A summed score was created and categorised into non-involved, low and high. Outcomes included 12-month and 24-month child growth, 12-month Bayley Scales of Infant and Toddler Development and 24-month Ages and Stages Questionnaire—Socioemotional. We used multivariable generalised linear models to estimate mean differences (MD) at 12 months (n=727) and 24 months (n=712). Inverse probability weighting was used to account for missingness and sampling.ResultsIn our sample, 68% of children lived with a grandmother, and most grandmothers were involved in caregiving. Greater 3-month grandmother involvement was positively associated with 12-month weight z-scores; however, greater involvement was associated with lower 24-month weight z-scores. High 12-month grandmother involvement was associated with improved 12-month cognitive (MD=0.38, 95% CI −0.01 to 0.76), fine motor skills (MD=0.45, 95% CI 0.08 to 0.83) and 24-month socioemotional development (MD=−17.83, 95% CI −31.47 to –4.19). No meaningful associations were found for length z-scores or language development.ConclusionIn rural Pakistan, grandmothers provide caregiving that influences early child development. Our findings highlight the complex relationship between grandmother involvement and child weight, and suggest that grandmothers may positively promote early child cognitive, fine motor and socioemotional development. Understanding how grandmother involvement affects child outcomes in early life is necessary to inform caregiving interventions.