In pediatric patients, the antibiotic use is affected by parental beliefs and practices; especially in countries where it is possible to acquire them without prescription. This study aims to describe the knowledge, attitudes, and practices on antibiotic use among parents of children from urban and peri-urban health care centers in Lima. A cross-sectional study was performed at 1 urban and 2 peri-urban health care centers selected in Lima, Peru. Parents of children below the age of 3 years answered a knowledge-attitudes-practices-validated questionnaire about antibiotic use and were categorized as high, moderate, and low knowledge regarding antibiotics. We analyzed potential determinants for low knowledge and having medicated their children with unprescribed antibiotics using bivariate and multivariate analyses. A total of 224 parents were enrolled, and 8% were categorized as low knowledge. Half of the parents could not recognize that antibiotics cannot cure viral infections, 59.4% disagreed with "antibiotics speed up recovery from a cold," and 53.2% stored antibiotics at home. Remarkably 23.5% of parents reported having medicated their children with antibiotics without prescription, which was associated with belonging to the peri-urban health care center, use of antibiotics by their children in the last 12 months, and having purchased antibiotics without physicians' prescription. An alarming overuse of antibiotics without prescription was described among children below the age of 3 years. Educational interventions, addressing parental attitudes and practices, and health policies should be developed to limit inappropriate antibiotic use especially in peri-urban communities.