Developmental scales for children aged 0-6 years are a particularly valuable resource for assessing developmental milestones in children. Most scales are developed based on a broad conceptual framework, and their metric validation is insufficient and of low quality. The aim of this systematic review is to analyse the psychometric quality of these tests and identify aspects in need of improvement. To this end, the PRISMA methodology and the WOS and ProQuest databases were used to search for articles addressing this topic. A total of 680 articles were identified, of which 72 were selected using the established inclusion and exclusion criteria. The results indicate a scarcity of independent studies on the statistical measurement of the scales. The selected articles are very heterogeneous and validate these tests using adaptations of common metrics. Most perform cross-cultural, concurrent, and prognostic validations of the tests. We conclude that the quality of the scale metrics and other common aspects of these tests need to be improved, particularly sample sparsity and heterogeneity, as well as cultural biases. We underline the importance of applying for advances in metrics for the construction of developmental scales and recommend the use of computerised versions to improve their ease of use and efficiency.