INTRODUCTION. It is well recognized internationally and in Spain that children from "vulnerable" family backgrounds participate less in quality early childhood education and care (ECEC). The objective of the article is to examine the barriers faced by families at social risk or in a situation of poverty for the enrollment of their 0 to 3 years old children in the first cycle of ECEC in different Spanish autonomous communities. METHOD. A qualitative study has been implemented in 2019 in five localities / metropolitan areas: Madrid, Valencia, Barcelona, the Basque Country and Seville. We have carried out semi-structured interviews with 35 families and discussion groups or group interviews with 40 technicians-key informants. The collected data have been transcribed and analyzed within a qualitative-inductive analytical logic, in particular following thematic analysis as outlined by Braun and Clarke (2012, 2021). RESULTS. A wide range of factors that prevent access to ECEC 0-3 in Spain are identified, including organizational-bureaucratic, ideological, financial, and those related to issues of family mobility or the child-protection system. In addition, the importance of each of these barriers varies according to the socioeconomic level of the families. DISCUSSION. Our results coincide with other studies in organizing barriers into different categories but, at the same time, they suggest a more complex relationship between these elements, especially in relation to the socio-economic circumstances of the families.