Final answer:
The nurse should encourage a child with a ruptured appendix to adopt the semi-Fowler's position, which helps reduce intra-abdominal pressure and alleviate discomfort, unlike other positions which may not be as effective or can increase pain.
Step-by-step explanation:
For a child with a ruptured appendix, the nurse should encourage the semi-Fowler's position. This position involves the child being partially sitting up with the head of the bed raised at about 30 to 45 degrees. It reduces intra-abdominal pressure and can help alleviate pain and discomfort. Lying flat on the back, or the supine position, may increase pressure on the appendix area, potentially causing more pain. The Sims' position (lying on one side with the lower arm behind the body and the upper thigh flexed) is not typically recommended in this case due to potential discomfort, and the orthopneic position (sitting up and bending forward with the support of a table or similar surface) is more for respiratory distress than abdominal issues.