To minimize children’s injuries due to car accidents, children must be transported in approved child restraint systems (CRS). The European Union optimized child protection by implementing R129 legislation for CRS in 2013. However, compliance with CRS recommendations after introduction of this newer standard has been scarcely evaluated. The main objectives of this study were to determine the prevalence of various types of CRS misuse and to investigate the use of ISOFIX and i-Size seats and parental knowledge regarding safe transportation of children in cars 5 years after the introduction of the newer R129 standard. During a cross-sectional observational study in the summer of 2018, parking lots of sites in the Netherlands were visited by researchers. Arriving or departing Dutch drivers who transported children under 9 years old were interviewed by means of a questionnaire and the misuse of CRS was directly observed using a checklist. Misuse was defined as CRS inappropriate for the child (based on height and weight) and/or CRS wrongly installed in the car and/or child improperly restrained in CRS. In total, 392 drivers and 470 children were included in the study. Results showed that 83% of the children were transported with at least 1 misuse of their CRS: 7% of the CRS were inappropriate for the child, 49% of the CRS were wrongly installed in the car, and 59% of the children were improperly restrained in a CRS. Most CRS were installed using the seat belt (88%) compared to ISOFIX (12%). ISOFIX usage did not result in less CRS installation misuse ( P = .338). The number of observed i-Size CRS was low ( n = 13, 3%). Most drivers were familiar with ISOFIX (76%), but only 13% of the drivers had heard of i-Size. For 9 out of 10 children, CRS misuse was observed. Many children were transported in an appropriate CRS, but various mistakes were made when installing the CRS in the car and restraining children in the CRS. Moreover, ISOFIX usage did not result in statistically significant less CRS installation misuse compared ...