Currently the majority of Child Restraint Systems (CRS) in the UK are approved to ECE Regulation 44 Amendment 03. This focuses on the crash performance of the CRS under frontal and rear impacts and does not include a sled side impact test.Although standards from Australia and New Zealand have for some time contained such a test, they do not include an element reproducing the effects of intrusion. Intrusion is a major factor in serious and fatal injuries to children in CRS. This paper describes a research program conducted to develop a simple side impact test which attempts to reproduce the effects of side structure intrusion on a CRS installed in a car on the struck side. A hinged door was mounted on the Middlesex University test sled, which, when opened contacted a CRS restrained on the ECE R 44 test seat mounted laterally on the sled. The door was opened under impact conditions when it struck an auxiliary impactor at the beginning of the sled deceleration phase. The chest and head response of ATDs restrained in current and prototype CRS was measured. These were compared with full-car side impacts conducted at TRL. The results suggested that the peak response of the ATD was representative of the car/barrier impacts but the energy input to the CRS as a function of time needs more development.