Background: Antibiotics remain the most prescribed medicine in children worldwide, but half of the prescriptions are unnecessary or inappropriate, leading to an increase in antibiotic resistance. This study aims to systemically review the effects of different Antimicrobial Stewardship Programmes (ASPs) on reducing the rates of both antibiotic prescriptions and changes in antimicrobial resistance, and on the economic impact in paediatric emergency departments (PED) and primary care settings. Materials and methods: Embase, MEDLINE, and Cochrane Library were systematically searched, combining Medical Subject Heading and free-text terms for ‘children’ and ‘antimicrobial’ and ‘stewardship’. The search strategy involved restrictions on dates (from 1 January 2007 to 30 December 2020) but not on language. Randomized controlled trials, controlled and non-controlled before and after studies, controlled and non-controlled interrupted time series, and cohort studies were included for review. The review protocol was registered at the PROSPERO International Prospective Register of Systematic Reviews: Registration Number CRD42021270630. Results: Of the 47,158 articles that remained after removing duplicates, 59 were eligible for inclusion. Most of the studies were published after 2015 (37/59, 62.7%) and in high-income countries (51/59, 86.4%). Almost half of the studies described the implementation of an ASP in the primary care setting (28/59, 47.5%), while 15 manuscripts described the implementation of ASPs in EDs (15/59, 25.4%). More than half of the studies (43/59, 72.9%) described the implementation of multiple interventions, whereas few studies considered the implementation of a single intervention. Antibiotic prescriptions and compliance with guidelines were the most frequent outcomes (47/59, 79.7% and 20/59, 33.9%, respectively). Most of the articles reported an improvement in these outcomes after implementing an ASP. Meanwhile, only very few studies focused on health care costs (6/59, 10.2%) and antimicrobial resistance (3/59 5.1%). Conclusion: The implementation of ASPs has been proven to be feasible and valuable, even in challenging settings such as Emergency Departments and Primary care.