Framed child seats secured with an adult seat belt have increasingly become the standard child restraint in UK vehicles. However, little work has been undertaken to investigate how the various design parameters affect the dynamic performance. This paper presents the results of a test programme designed to address this question. Parameters such as system centre of gravity, adult belt route, shell inclination and footprint area were varied on a surrogate child restraint, which was subjected to dynamic impact tests in general accordance with ECE R44. The tests were repeated with the child restraint anchored both with adult lap and lap and diagonal belts. The performance was evaluated using the values of 3ms chest acceleration and head forward excursion on the test dummy. A distinction in the effect of each of the parameters was found between the child restraint anchored with a lap belt and that anchored with a 3-point belt. The lowest value of chest acceleration (40g) was observed for the lap belt restrained frame seat with the largest base area while the lowest head excursion was also seen with this arrangement but with the addition of a top tether. Exploring the use of energy absorbing top tethers is suggested.