Background: Primary healthcare, particularly Indigenous-led services, are well placed to deliver services that reflect the needs of Indigenous children and their families. Important characteristics identified by families for primary health care include services that support families, accommodate sociocultural needs, recognise extended family child-rearing practices, and Indigenous ways of knowing and doing business. Indigenous family-centred care interventions have been developed and implemented within primary healthcare services to plan, implement, and support the care of children, immediate and extended family and the home environment. The delivery of family-centred interventions can be through environmental, communication, educational, counselling, and family support approaches. Objectives: To evaluate the benefits and harms of family-centred interventions delivered by primary healthcare services in Canada, Australia, New Zealand, and the USA on a range of physical, psychosocial, and behavioural outcomes of Indigenous children (aged from conception to less than five years), parents, and families. Search methods: We used standard, extensive Cochrane search methods. The latest search date was 22 September 2021. Selection criteria: We included randomised controlled trials (RCTs), cluster RCTs, quasi-RCTs, controlled before-after studies, and interrupted time series of family-centred care interventions that included Indigenous children aged less than five years from Canada, Australia, New Zealand, and the USA. Interventions were included if they met the assessment criteria for family-centred interventions and were delivered in primary health care. Comparison interventions could include usual maternal and child health care or one form of family-centred intervention versus another. Data collection and analysis: We used standard Cochrane methods. Our primary outcomes were 1. overall health and well-being, 2. psychological health and emotional behaviour of children, 3. physical health and developmental health outcomes of children, 4. family health-enhancing lifestyle or behaviour outcomes, 5. psychological health of parent/carer. 6. adverse events or harms. Our secondary outcomes were 7. parenting knowledge and awareness, 8. family evaluation of care, 9. service access and utilisation, 10. family-centredness of consultation processes, and 11. economic costs and outcomes associated with the interventions. We used GRADE to assess the certainty of the evidence for our primary outcomes. Main results: We included nine RCTs and two cluster-RCTs that investigated the effect of family-centred care interventions delivered by primary healthcare services for Indigenous early child well-being. There were 1270 mother–child dyads and 1924 children aged less than five years recruited. Seven studies were from the USA, two from New Zealand, one from Canada, and one delivered in both Australia and New Zealand. The focus of interventions varied and included three studies focused on early childhood caries; three on childhood obesity; two on child behavioural problems; and one each on negative parenting patterns, child acute respiratory illness, and sudden unexpected death in infancy. Family-centred education was the most common type of intervention delivered. Three studies compared family-centred care to usual care and seven studies provided some 'minimal' intervention to families such as education in the form of pamphlets or newsletters. One study provided a minimal intervention during the child's first 24 months and then the family-centred care intervention for one year. No studies had low or unclear risk of bias across all domains. All studies had a high risk of bias for the blinding of participants and personnel domain. Family-centred care may improve overall health and well-being of Indigenous children and their families, but the evidence was very uncertain. The pooled effect estimate from 11 studies suggests that family-centred care improved the overall health and well-being of Indigenous children and their families compared no family-centred care (standardised mean difference (SMD) 0.14, 95% confidence interval (CI) 0.03 to 0.24; 2386 participants). We are very uncertain whether family-centred care compared to no family-centred care improves the psychological health and emotional behaviour of children as measured by the Infant Toddler Social Emotional Assessment (ITSEA) (Competence domain) (mean difference (MD) 0.04, 95% CI −0.03 to 0.11; 2 studies, 384 participants). We assessed the evidence as being very uncertain about the effect of family-centred care on physical health and developmental health outcomes of children. Pooled data from eight trials on physical health and developmental outcomes found there was little to no difference between the intervention and the control groups (SMD 0.13, 95% CI −0.00 to 0.26; 1961 participants). The evidence is also very unclear whether family-centred care improved family-enhancing lifestyle and behaviours outcomes. Nine studies measured family health-enhancing lifestyle and behaviours and pooled analysis found there was little to no difference between groups (SMD 0.16, 95% CI −0.06 to 0.39; 1969 participants; very low-certainty evidence). There was very low-certainty evidence of little to no difference for the psychological health of parents and carers when they participated in family-centred care compared to any control group (SMD 0.10, 95% CI −0.03 to 0.22; 5 studies, 975 parents/carers). Two studies stated that there were no adverse events as a result of the intervention. No additional data were provided. No studies reported from the health service providers perspective or on outcomes for family's evaluation of care or family-centredness of consultation processes. Authors' conclusions: There is some evidence to suggest that family-centred care delivered by primary healthcare services improves the overall health and well-being of Indigenous children, parents, and families. However, due to lack of data, there was not enough evidence to determine whether specific outcomes such as child health and development improved as a result of family-centred interventions. Seven of the 11 studies delivered family-centred education interventions. Seven studies were from the USA and centred on two particular trials, the 'Healthy Children, Strong Families' and 'Family Spirit' trials. As the evidence is very low certainty for all outcomes, further high-quality trials are needed to provide robust evidence for the use of family-centred care interventions for Indigenous children aged less than five years.