Analysing a recent trend in interface design, this chapter examines the question of software and the interface in relation to the aesthetic of the postdigital. To do this, it first looks at contemporary trends in online design, such as ‘flat design’, created to address adults while looking as if it should be for children. After having described the phenomenon of infantilization in digital environments, the second part of the chapter looks into forces that produce it. Why does it occur especially in a technological environment, and what is the specificity of its occurrence? Considering historical influences on interface design to answer these questions — computer scientists such as Alan Kay or Seymour Papert were informed by theories of Jean Piaget — we find an ambiguous figure at work: there is a fine dividing line within infantilization, between the adaptation of learning to ‘children of all ages’ to emancipate users and manipulating them, engendering stupidity as the desirable state they should be in.