Small-quantity lipid-based nutrient supplements (SQ-LNSs) were designed to provide multiple micronutrients within a food base that also provides energy, protein, and essential fatty acids, targeted towards preventing malnutrition in vulnerable populations. Previous meta-analyses demonstrated beneficial effects of SQ-LNSs on child growth, anemia, and mortality. To further examine the efficacy and effectiveness of SQ-LNSs, and explore study-level and individual-level effect modifiers, we conducted an individual participant data meta-analysis of 14 randomized controlled trials of SQ-LNSs provided to children 6-24 mo of age (n > 37,000). We examined growth, development, anemia, and micronutrient status outcomes. Children who received SQ-LNSs had a 12-14% lower prevalence of stunting, wasting, and underweight; were 16-19% less likely to score in the lowest decile for language, social-emotional, and motor development; had a 16% lower prevalence of anemia; and had a 64% lower prevalence of iron-deficiency anemia compared with control group children. For most outcomes, beneficial effects of SQ-LNSs were evident regardless of study-level characteristics, including region, stunting burden, malaria prevalence, sanitation, water quality, duration of supplementation, frequency of contact, or average reported compliance with SQ-LNSs. For development, the benefits of SQ-LNSs were greater in populations with higher stunting burden, in households with lower socioeconomic status, and among acutely malnourished children. For hemoglobin and iron status, benefits were greater in populations with higher anemia prevalence and among acutely malnourished children, respectively. Thus, targeting based on potential to benefit may be worthwhile for those outcomes. Overall, co-packaging SQ-LNSs with interventions that reduce constraints on response, such as the prevention and control of prenatal and child infections, improving health care access, and promotion of early child development, may lead to greater impact. Policymakers and program planners should consider including SQ-LNSs in strategies to reduce child mortality, stunting, wasting, anemia, iron deficiency, and delayed development. This study was registered at www.crd.york.ac.uk/PROSPERO as CRD42019146592, CRD42020159971, and CRD42020156663.