Effects of formal aquatic activities on health and developmental outcomes in infants and toddlers younger than 36 months: a systematic review and meta-analysis

Aims To systematically review and meta-analyze controlled evidence on the effects of formal aquatic activities on health and developmental outcomes in infants and toddlers younger than 36 months. Background Formal aquatic activities—including infant swimming, neonatal swimming, hydrotherapy, and warm-water bathing—are increasingly used in early-life care, yet existing studies vary in populations, intervention formats, and outcome measures, making overall effects difficult to determine. A structured synthesis is needed to clarify their potential role in early health and development. Methods We conducted an updated search of PubMed, Ovid MEDLINE(R) ALL, EMBASE, PsycINFO, Scopus, SportDiscus, Web of Science, and EBSCOhost (December 2022 to May 25, 2026) and CNKI (inception to May 25, 2026). Controlled studies evaluating formal aquatic activities in infants or toddlers younger than 36 months were eligible. Outcomes were coded and organized using the WHO International Classification of Functioning, Disability and Health for Children and Youth (ICF-CY) framework. Random-effects meta-analyses pooled standardized mean differences (SMDs) for continuous outcomes and risk ratios (RRs) for binary developmental classification outcomes. Sensitivity and subgroup analyses were conducted where heterogeneity was substantial. Results 25 studies (3,526 participants; 1,822 aquatic intervention, 1,704 comparator) were included; 22 contributed to the meta-analysis. Across six outcome domains, 87 effect sizes were synthesized. Aquatic activities showed favourable effects on: neurodevelopmental and motor function (SMD = 0.96, 95% CI 0.78–1.15), growth and anthropometry (SMD = 0.54, 95% CI 0.44–0.63), physiological regulation and safety (SMD = 0.85, 95% CI 0.49–1.22), beneficial developmental classification (RR = 1.45, 95% CI 1.29–1.62), jaundice burden and bilirubin metabolism (SMD = 2.31, 95% CI 1.37–3.26), and feeding, stool transition, and digestion (SMD = 0.81, 95% CI 0.61–1.01). Heterogeneity was highest for jaundice-related outcomes; sensitivity and subgroup analyses confirmed the favourable direction of effects. Conclusions This ICF-CY-informed systematic review and meta-analysis suggests that formal aquatic activities may have beneficial effects across multiple health and developmental domains in infants and toddlers under 36 months. These findings support using aquatic activities as a complementary approach in early-life care, while underscoring the need for more rigorous randomized trials, standardized intervention protocols, and longer follow-up to strengthen the evidence base.