Multimodal Intervention and Child Passenger Safety Guideline Adherence in Young Children: A Sequential, Multiple-Assignment, Randomized Clinical Trial.

Importance: Suboptimal child passenger safety behaviors are common despite the availability of effective child restraint systems (CRS), with national guidelines promoting-and state laws requiring-their use. Objective: To compare 6-month guideline adherence following the Tiny Cargo, Big Deal, Abróchame Bien, Cuídame Bien (TCBD/ABCB) intervention vs enhanced usual care (EUC); assess 12-month maintenance effect; and evaluate sequential, multiple-assignment, randomized trial (SMART) phase 2 outcomes by intervention intensity. Design, Setting, and Participants: This randomized clinical trial using a SMART study design was conducted at 1 pediatric emergency department (ED), 1 community ED, and 2 urgent care centers in metropolitan Chicago, Illinois, from February 2020 to August 2022. Eligible caregivers spoke English or Spanish, lived in Illinois, owned a smartphone, traveled weekly with their child (aged 6 months to younger than 11 years), and reported suboptimal child passenger safety behaviors. Of 5416 caregivers who were screened, 1517 were potentially eligible. Data analysis occurred from October 2024 to March 2025. Interventions: Phase 1 included basic TCBD/ABCB (remote motivational interviewing [MI] plus tailored mobile health [mHealth]) vs EUC (text message photograph requests, follow-up activity reminders, and corrective feedback only for predefined critical errors). In phase 2, participants exposed to TCBD/ABCB but who were nonadherent at 6 months received high-intensity (second remote MI session plus extra text messages) or low-intensity (mHealth alone) interventions. Main Outcome and Measures: The primary outcome was guideline adherence, a dichotomous measure of all 3 criteria: (1) appropriate CRS, (2) back seat location, and (3) never unrestrained. Outcomes were assessed at 6 and 12 months using logistic regression with prevalence differences, adjusted for randomization strata, caregiver gender, race, and ethnicity. Results: In phase 1, there were 474 participants (mean [SD] caregiver age, 36.1 [6.2] years; 443 mothers [93.5%]; 52 [11.0%] preferred Spanish]) of whom 342 were randomized to basic TCBD/ABCB and 132 to EUC. Among participants with 6-month follow-up data, 131 of 278 caregivers receiving TCBD/ABCB (47.1%; 95% CI, 41.3% to 53.0%) vs 38 of 118 receiving EUC (32.2%; 95% CI, 23.8% to 40.6%) were guideline adherent (absolute change in treatment response, 13.1%; 95% CI, 3.6% to 22.6%; P = .007) with 12-month maintenance effects (adjusted prevalence difference, 39.2%; 95% CI, 26.5% to 51.9%; P < .001). In phase 2, 185 participants who received TCBD/ABCB and were not guideline adherent were rerandomized to high-intensity (87 participants) or low-intensity (84 participants) intervention. High-intensity TCBD/ABCB had no effect compared with low-intensity TCBD/ABCB (adjusted prevalence difference, -3.9%; 95% CI -17.9% to 10.1%; P = .59). Conclusions and Relevance: In this randomized clinical trial of caregivers, TCBD/ABCB was associated with improved adherence to child passenger safety guidelines with lasting effects among those caregivers who were adherent at 6 months. These findings suggest that this remote precision prevention intervention against a leading cause of death may be adaptable to other settings. Trial Registration: ClinicalTrials.gov Identifier: NCT04238247.