Over the years, the Spanish education authorities have proposed various measures, such as the creation of Open Educational Resources (OERs), to guarantee the inclusion of all students in the education system. However, the literature on this topic indicates the persistence of certain challenges relating to the accessibility of OERs. In this regard, Universal Design for Learning (UDL) is presented as a possible solution to this problem as it advocates the personalisation of learning and facilitates the achievement of universal digital literacy. This study seeks to investigate the accessibility of OERs' design for those early stages in education that are managed by the Spanish education authorities. To this end, a guide of indicators has been designed to assess OERs in accordance with the principles of UDL. The sample is made up of 67 OERs, selectively based on a number of requirements. This study uses a quantitative and exploratory research methodology for the analysis of the data obtained. The main findings highlight the shortcomings of OERs in terms of accessibility, adaptability and universality, demonstrating that OERs do not respond to the principles of UDL.