Pediatric ear, nose, and throat (ENT) surgery is very common, and its outcomes may improve with family education. In this regard, mobile health (mHealth) applications (apps), which are on the rise due to digital transformation, can be beneficial in healthcare. This study outlines the user-centered design and development of a mHealth app (version 5.15.0) to support family caregivers during the perioperative process of pediatric ENT surgery. Conducted over two years in an Italian maternal and child health hospital (January 2020–May 2022), the study employed a participatory design method based on the Information System Research (ISR) framework and guided by the principles of Slow Medicine. Utilizing the Relevance, Rigor, and Design cycles of the ISR framework, the mHealth app’s content, functionalities, and technical features were defined and developed. A committee of fifteen experts guided the process with input from 25 family caregivers and 24 healthcare providers enrolled in the study. The mHealth app content was structured around five crucial educational moments characterizing the ENT perioperative period, providing evidence-based information on surgical procedures, strategies for preparing children for hospitalization and surgery, pain management, and post-discharge care. The mHealth app featured a function that sends customized notifications to guide caregivers at specific perioperative stages. The development of mHealth apps by implementing a rigorous, participatory, and Slow design process can foster accessible and family-centered information and care in the field of maternal and child health and beyond.