BackgroundFruit and vegetable (FV) consumption in children in the United States (US) is very low. Adequate FV consumption is required for proper development during childhood, and dietary habits are established during preschool-age and tend to persist into adulthood. As most U.S. preschool-aged children attend childcare or preschool, this may be an opportune time and setting to conduct interventions to improve FV intake. These interventions should be based in theory and use behavior change techniques (BCTs) to explain mechanisms for expected change. To date, no published reviews have examined the effectiveness of childcare- or preschool-based FV interventions in preschoolers and their use of theoretical frameworks and BCTs.MethodsThis systematic review was completed adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Inclusion criteria were randomized controlled trials (RCTs) published between 2012 and 2022 of interventions to improve diet or FV intake in preschoolers (aged 2–5 years) in childcare or preschool-settings. A search of four databases was conducted between in September 2022 using search terms pertaining to the study’s primary aim (FV consumption), age group (preschool-aged), settings (US childcare or preschool settings), and study design (RCT). Additional criteria were objective measures of FV consumption or skin carotenoids, as a proxy for FV intake. Included studies were narratively synthesized based on intervention type, measured effect, and use of theory and BCTs.ResultsThe search resulted in six studies that reported on nine interventions. Overall, six interventions increased FV intake, of which five used nutrition education and one manipulated the feeding environment. Among the three interventions with no measured effect, two manipulated the feeding environment and one used peer modeling. Effective studies used at least three BCTs, though no pattern was observed between use of theory or BCTs and intervention effect.ConclusionsWhile several studies have shown promising results, the limited number of studies identified in this review highlights key gaps in this field: there is a need for studies to test FV interventions in US childcare settings that use objective measures of FV intake, directly compare intervention components and BCTs, are theory-based, and assess long-term behavior change.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12966-023-01472-8.