This study explored the experiences of public health nurses (PHN) in preventing obesity in preschool children and following national guidelines. We used a descriptive qualitative design with an online open-ended questionnaire based on vignettes describing fictitious practical situations during the follow-up of children presenting with overweight issues in child health clinics. Following qualitative content analysis, we identified one main theme: Strong but complex feelings of responsibility toward supporting parents in preventing obesity in preschool children and adhering to the guidelines. We also identified four subthemes: (a) Difficulties in deciding if the child’s weight is a concern. (b) Challenges with meeting children’s healthcare needs when weight is a concern. (c) Approaches for engagement and caring weight talks with parents. (d) The need for resources and interdisciplinary collaboration. PHNs suggested improvements for preventing childhood obesity and called for municipal prioritizing of organizational and personnel-related resources to ensure PHNs can efficiently follow national guidelines.