Dental caries, a common chronic disease of childhood, is associated with adverse health and economic consequences for infants and their families. Socioeconomically disadvantaged children have a higher risk of early childhood caries (ECC). This review updates one published in 2019. To assess the effects of interventions undertaken with pregnant women, new mothers or other primary caregivers of infants in the first year of life, for preventing ECC (from birth to six years). We searched Cochrane Oral Health's Trials Register, Cochrane Pregnancy and Childbirth's Trials Register, CENTRAL, MEDLINE (Ovid), Embase (Ovid), CINAHL EBSCO, the US National Institutes of Health Ongoing Trials Register (clinicaltrials.gov) and WHO International Clinical Trials Registry Platform (apps.who.int/trialsearch). The latest searches were run on 3 January, 2023. Randomised controlled trials (RCTs) comparing interventions with pregnant women, or new mothers and other primary caregivers of infants in the first year of life, against standard care, placebo or another intervention, reporting on a primary outcome: caries presence in primary teeth, dmfs (decayed, missing, filled primary surfaces index), or dmft (decayed, missing, filled teeth index), in children up to six years of age. Intervention types include clinical, oral health promotion/education (hygiene education, breastfeeding and other dietary advice) and policy or service. Two review authors independently assessed study eligibility, extracted data, assessed risk of bias, and assessed certainty of evidence (GRADE). We included 23 RCTs (5 cluster-randomised), involving 25,953 caregivers (mainly mothers) and their children. Fifteen trials assessed oral health education/promotion interventions against standard care. Six trials assessed a clinical intervention for mother dentition, against placebo, or a different type of clinical intervention. Two trials assessed oral health/education promotion plus clinical intervention (for mother's dentition) against standard care. At most, five trials (maximum of 1326 children and 130 mothers) contributed data to any comparison. Enamel-only caries were included in the diagnosis of caries in some studies. For many trials, the risk of bias was unclear due to lack of methodological details reported. In thirteen trials, participants were socioeconomically disadvantaged. No trial indicated receiving funding that was likely to have influenced their results. Oral health education/promotion interventions Child diet and feeding practice advice versus standard care: We observed a probable 15 per cent reduced risk of caries presence in primary teeth with the intervention (RR 0.85, 95% CI 0.75 to 0.97; 3 trials; 782 participants; moderate-certainty evidence), and there may be a slightly lower mean dmfs (MD -0.29, 95% CI -0.58 to 0; 2 trials; 757 participants; low-certainty evidence); however, the evidence is very uncertain regarding the difference between groups in mean dmft (MD -0.90, 95% CI -1.85 to 0.05; 1 trial; 340 participants; very low-certainty evidence). Breastfeeding promotion and support versus standard care: We observed little or no difference between groups in the risk of caries presence in primary teeth (RR 0.96, 95% CI 0.89 to 1.03; 2 trials; 1148 participants; low-certainty evidence) and in mean dmft (MD -0.12, 95% CI -0.59 to 0.36; 2 trials; 652 participants; low-certainty evidence). dmfs was not reported. Child diet advice compared with standard care: We are very uncertain about the effect on the risk of caries presence in primary teeth (RR 1.08, 95% CI 0.34 to 3.37; 1 trial; 148 participants; very low-certainty evidence). dmfs and dmft were not reported. Oral hygiene, child diet and feeding practice advice versus standard care: The evidence is very uncertain about the effect on the risk of caries presence in primary teeth (RR 0.73, 95% CI 0.50 to 1.07; 5 trials; 1326 participants; very low-certainty evidence) and there maybe little to no difference in mean dmfs (MD -0.87, 95% CI -2.18 to 0.43; 2 trials; 657 participants; low-certainty evidence) and mean dmft (MD -0.30, 95% CI -0.96 to 0.36; 1 trial; 187 participants; low-certainty evidence). High-dose versus low-dose vitamin D supplementation during pregnancy: We are very uncertain about the effect on risk of caries presence in primary teeth (RR 0.99, 95% CI 0.70 to 1.41; 1 trial; 496 participants; very low-certainty evidence). dmfs and dmft were not reported. Clinical interventions (for mother dentition) Chlorhexidine (CHX, a commonly prescribed antiseptic agent) or iodine-NaF application and prophylaxis versus placebo: We are very uncertain regarding the difference in risk of caries presence in primary teeth between antimicrobial and placebo treatment for mother dentition (RR 0.97, 95% CI 0.80 to 1.19; 3 trials; 479 participants; very low-certainty evidence). No trial reported dmfs or dmft. Xylitol compared with CHX antimicrobial treatment: We are very uncertain about the effect on caries presence in primary teeth (RR 0.62, 95% CI 0.27 to 1.39; 1 trial, 96 participants; very low-certainty evidence), but we observed there may be a lower mean dmft with xylitol (MD -2.39; 95% CI -4.10 to -0.68; 1 trial, 113 participants; low-certainty evidence). No trial reported dmfs. Oral health education/promotion plus clinical interventions (for mother dentition) Diet and feeding practice advice for infants and young children plus basic dental care for mothers compared with standard care: We are very uncertain about the effect on risk of caries presence in primary teeth (RR 0.44, 95% CI 0.05 to 3.95; 2 trials, 324 participants; very low-certainty evidence) or on mean dmft (1 study, not estimable). No trial reported dmfs. No trials evaluated policy or health service interventions. There is moderate-certainty evidence that providing advice on diet and feeding to pregnant women, mothers or other caregivers with children up to the age of one year probably leads to a slightly reduced risk of early childhood caries (ECC). The remaining evidence is low to very-low certainty and is insufficient for determining which, if any, other intervention types and features may be effective for preventing ECC, and in which settings. Large, high-quality RCTs of oral health education/promotion, clinical, and policy and service access interventions, are warranted to determine the effects and relative effects of different interventions and inform practice. We have identified 13 ongoing studies. Future studies should consider if and how effects are modified by intervention features and participant characteristics (including socioeconomic status).