Historically, instead of conducting well-designed research studies in the pediatric population, drug monographs indicate that safety and efficacy in children have not been evaluated. Among the main challenges in clinical trials for children, ethical issues occupy a special place, as they arise at almost all stages — from clinical trials to extrapolation. In the article, the authors present the history of clinical research in pediatrics and neonatology, how the view of involving children in clinical trials has changed, the specific ethical problems of children’s participation in clinical trials, legislative initiatives and other agreed measures taken and what they have led to. The ethical issues of microdosing in pediatrics, methods for the first-in-pediatric dose selection, issues of acceptability and drug development for the treatment of rare diseases are discussed separately. Conducting trials in the most vulnerable pediatric groups — newborns and premature newborns — is presented in detail. The potential reasons for trial failures in children are presented with specific examples.