Before surgery, children were asked whether they enjoyed listening to music and what styles of music they liked.

• A 30-minute playlist was created using songs from the music pool based on the child's preferences.
• Children were informed about postoperative mobility and which movements they would be expected to perform.

No music Listening

All procedures required for developing a music pool to be used for music listening intervention in children undergoing appendectomy were completed and are outlined as follows:

• Children were asked about their music preferences.
• Songs were selected from the Ministry of National Education's music books.
• Music with proven effectiveness was selected from music platforms.
• A music pool was created by the researcher based on these inputs.
• Expert opinions were obtained from 12 academicians and 10 healthy children regarding the music pool.
• Necessary revisions were made in line with expert feedback, and the final version of the music pool was determined.
• A pilot application was conducted (data from the pilot were not included in the main data set).
• Children were randomly assigned to the music and control groups using randomization (https://www.random.org).
• A neutral observer (not the researcher/a blinded observer) was trained to administer the scales after the music intervention

Completed by the patient. The six-item scale evaluates three key postoperative mobilization activities: sitting on the bedside, standing at the bedside, and walking in the patient room. Each item is scored between 0 and 15, with the total scale score ranging from 0 to 90. Higher scores indicate greater pain and difficulty during mobilization, while lower scores reflect reduced pain and ease of movement.

Completed by the observer. The Observer Mobility Scale developed by the same authors as a complementary dimension to the Patient Mobility Scale, evaluates objective observations of the same three postoperative activities. Each item is scored on a scale of 1 to 5, with a total score range of 3 to 15. Higher scores reflect poorer mobility performance, while lower scores indicate better and more adequate postoperative mobility.