In a modern society children are exposed to many different hazards. Different types of safety barriers are often used to protect children from life-endangering accidents such as falling from great heights or falling into swimming pools. Children have a natural curiosity and climbing is a natural behaviour for them. They can and will climb objects in their environment and as they grow older their climbing ability improves. This study focuses on children’s ability to climb barriers and the barrier’s effectiveness for children of ages 4 to 6 years. The aim of the study is to obtain complementary knowledge as input to revised standards and recommendations in Europe in order to improve child safety in the built environment. An experimental study of child safety barriers has been carried out with 157 participating children in the ages 4-6 years. The relatively large sample size is necessary because there is a considerable variation in both mental and physical abilities in the age groups considered. The designs of the barriers used in the study have been chosen based on a literature survey. In this limited study it has been considered necessary to focus on a few archetype barriers, which are considered most effective, and to vary properties of these within the limits which can be accepted from economic and aesthetic points of view. Since the most able children in the age groups studied can climb such barriers, barriers must be seen as a method of increasing the time for children to enter a dangerous area rather than as providing complete safety. Hence, the time it takes for a successful climb is a relevant parameter to study. The results show that simple barriers with vertical bars or solid panels and heights 1.1 m – 1.2 m can be climbed by around half the children within 30 seconds also in the lower age groups, and that the difference in height is not very significant. The most effective barrier in this study is the one which is inclined towards the climber.