Background: Preterm birth is associated with elevated childhood blood pressure (BP), but underlying mechanisms and preventive strategies remain unclear. Objectives: To investigate whether amino acids mediate the inverse association between gestational age (GA) and BP, and to assess how initial breastfeeding modulates this pathway . Methods: Data from 67 ,246 mother-child dyads across three prospective cohorts (Shanghai Birth Cohort, Collaborative Perinatal Project, Avon Longitudinal Study) were analyzed using metabolome-wide association, multivariable regression, mediation analysis, meta-analysis, and restricted cubic splines. Results: GA was inversely associated with systolic BP (SBP; pooled β = -0.23) and diastolic BP (DBP; β = -0.11). Phenylalanine (Phe) and tyrosine (Tyr) were positively associated with BP and inversely with GA. Phe and Tyr mediated 16% and 39% of the GA-SBP association, respectively . In breastfed infants, these mediation proportions decreased to 8% and 21%. Tryptophan mediated 9% (SBP) and 21% (DBP), and total aromatic amino acids mediated 25% (SBP) and 42% (DBP) of the BPlowering effect of breastfeeding. Initial breastfeeding conferred greater prehypertension/hypertension risk reduction in preterm (ORs: 0.56/0.48) versus term infants (ORs: 0.81/0.79). Conclusions: Aromatic amino acids mediate GA-associated BP elevation in children. Early breastfeeding mitigates this risk in preterm infants, suggesting a critical primary prevention strategy .