The current study aimed to understand the perceptions and experiences of Iranian parents and principals of preschool children on weight management based on the PRECEDE-PROCEED Model (PPM), a comprehensive structure for assessing health needs for designing, implementing, and evaluating health promotion, and other public health programs. PRECEDE provides a structure for planning a targeted and focused public health program, and PROCEED provides a structure for implementing and evaluating the program. Data were gathered from 17 preschoolers’ parents and two principals using semi-structured interviews in the preschool setting in Tehran, the capital of Iran, in 2019. Data were analyzed manually through directed content analysis based on constructs in phases two and three of the PPM, simultaneously with data collection. This study identified genetic, behavioral (e.g., food preferences, physical activity, sedentary behaviors, the effect of parents’, peers’, principals’ and teachers’ behavior and also influence of grandparents’ and neighbors’ behaviors) and environmental (e.g., home, grandparents’ home and preschool) factors from the epidemiological construct. Also, predisposing (e.g., child’s attitude, parent’s and principals’ attitude, as well as parents’ knowledge and parents’ and principals’ beliefs), enabling (e.g., parental skills and skills of the principals and teachers, rules and laws in the preschools, and availability), and reinforcing (e.g., family support and influences, teachers’ encouragement and influences, and peers’ influences) factors were identified from the educational and ecological construct. Additionally, “quality of child-parent relationship” was determined as a new factor affecting preschoolers’ weight management promotion; however, it was not in the PPM. In the study, parents’ and principals’ experiences regarding preschoolers’ weight management promotion confirmed the genetic, behavioral, environmental, predisposing, enabling and reinforcing factors of the PPM. “Quality of child-parent relationship” factor may be related to the culture and family relationship type of Iranian people, which is suggested to be investigated in future studies.