Suboptimal compliance with child restraint system (CRS) recommendations can increase risk for injury or death in a motor vehicle crash. The purpose of this study was to examine scenarios associated with incomplete CRS use and non-use in children ages 4⁻10 years. We used a cross-sectional online survey with a convenience sample of parent/caregivers from the United States, age ≥18 years, with a child age 4⁻10 years in their home, who could read and spoke English, and drove child ≥6 times in previous three months. We used descriptive statistics and Mann-Whitney U to describe and compare the distribution of responses to situational use of CRSs among car seat users and booster seat users. We also used descriptive statistics and the Mann-Whitney U to describe and compare the distribution of responses to carpooling items among booster seat users and non-booster seat users. There were significant differences among those who reported most often using booster seats (n = 282) and car seats (n = 127) in situations involving rental cars, driving just around the corner, car too crowded to fit the CRS, not enough CRSs in the vehicle, the CRS is missing from the car, or the child is in someone else's car without a CRS ( < 0.05). Among those who reported most often using booster seats and who carpooled other children (n = 159), 71.7% (n = 114) always used a booster seat for their own child. When carpooling other children, booster seat users were significantly more likely to use booster seats for other children ages 4⁻10 than the non-booster seat users ( < 0.01). Continued education and programs surrounding CRS use is critical, particularly for children who should be in booster seats.