Aim To identify child and parent outcomes relevant to having a gastrostomy, and to specify outcomes believed to be particularly salient to type of diet (formula vs blended food). Method Twenty parents, two children (both 12y), and 41 professionals (dietitians n=10; nurses n=12; paediatricians n=12; speech and language therapists n=7)) were recruited. Parents and children were interviewed; professionals participated in focus groups. Children (2–18y) represented included those on formula (n=11), blended‐food (n=7), and mixed (n=2) diets. All had been tube‐fed for at least 6 months. Neurological, genetic, and metabolic conditions were represented. Results Participants identified a range of children’s outcomes relevant to a gastrostomy, including physical health, gastrointestinal symptoms, sleep, and time spent feeding. The children described experiences of exclusion caused by being tube‐fed. Time, sleep, and emotional health were regarded as most salient to understanding parents’ gastrostomy outcomes. Participants believed type of diet would most likely effect gastrointestinal symptoms, time spent feeding, sleep, and physical health. Interpretation Findings indicate a number of refinements to, and allow further specification of, the current ‘initial’ core outcome set for tube‐fed children. Findings also have implications for choice of outcomes measures. Further qualitative research with children and young people is needed. What this paper adds Sleep is a key outcome for children and parents. Gastrointestinal symptoms and physical health were regarded as outcomes most likely to be affected by type of diet. Well‐being and participation were identified as key distal outcomes. Gastrostomies are complex interventions. Further specification of the core outcome set is possible. What this paper adds Sleep is a key outcome for children and parents. Gastrointestinal symptoms and physical health were regarded as outcomes most likely to be affected by type of diet. Well‐being and participation were identified as key distal outcomes. Gastrostomies are complex interventions. Further specification of the core outcome set is possible. This article is commented on by Nimmo on page 1014 of this issue.