Background: Elevated blood pressure (BP) in childhood is associated with cardiovascular risk, but its molecular lipid correlates remain poorly characterized. We investigated the association of plasma lipid species and patterns with concurrent and longitudinal BP phenotypes in school-aged children. Methods: In the Belgian ENVIRONAGE prospective birth-cohort, 195 children aged 9 to 12 years were examined between July 2021 and September 2024. A total of 1,232 plasma lipid species were quantified using liquid chromatography-electrospray ionization-tandem mass spectrometry. Associations with systolic and diastolic BP percentiles were examined using multivariable linear regression with permutation-based family-wise error rate (FWER) correction. Lipid-set enrichment analysis, with P values from sample permutation to account for correlation among lipid species, evaluated coordinated associations. Significant findings were examined across longitudinal BP patterns in 177 children with BP measured at ages 4-6 and 9-12. Findings: Each 1-SD increase in triglyceride (TG) 58:9 fatty acyl (FA) 22:4 was associated with 7.36 higher systolic BP percentile points (95% CI=3.91-10.80; P_FWER=0.03). TG 58:9 FA 22:4 was associated with incident (OR=2.78; 95% CI=1.33-5.79) and persistent (OR=2.14; 95% CI=1.22-3.77), but not resolved elevated BP vs stable-normal BP. Among lipid sets, species with a total carbon number of 38, mainly PC and PE, were inversely enriched with diastolic BP percentile. Interpretation: Childhood BP was associated with higher levels of a highly polyunsaturated long-chain TG, closely related to current BP elevation and not elevated among children whose BP had normalized.