In recent years, there has been considerable investment at the European Union level in expanding early childhood education and care (ECEC) facilities. In line with this quantitative substantial initiative, research and social policies are increasingly focusing on the quality of such facilities. High quality depends, among other things, on well-trained early childhood educators. This poses a dilemma for early childhood educators for various reasons; there is a shortage of skilled early childhood professionals, so that low-skilled staff are also being employed in early childhood education facilities. Online formats for professional development can contribute to the professionalisation of the ECEC system through vocational training. Since these formats are designed and produced to high professional and technical standards, they can be cost-effective thanks to their multiple uses and because they can often be completed by participants independent of time and location. This article presents an empirically studied blended e-learning training format based on the principles of co-constructivist didactics. The content focuses on the quality of interaction between early childhood professionals and children. Before and after the training course was completed, standardised non-participant observations were conducted in Austrian, German, Hungarian, Slovenian, Italian, and Portuguese early childhood education and care institutions. The before/after measurements (N = 43) showed a significant effect on the quality of interaction between the early childhood professionals and the children.