Final answer:
Morphine is generally the best option for patient-controlled analgesia (PCA) for children in the immediate postoperative period due to its potency and ability to be self-administered by patients as needed for pain control.
Step-by-step explanation:
When selecting the best choice for patient-controlled analgesia (PCA) for a child in the immediate postoperative period, morphine is generally considered the most appropriate option. Morphine is a potent opioid that is frequently used to alleviate severe pain before and after surgical procedures. It acts directly on the central nervous system to decrease the feeling of pain and can be tailored to the needs of individual patients via PCA, allowing them to self-administer the medication as needed for pain control. Unlike morphine, codeine is often prescribed for mild to moderate pain, methadone is commonly used in the management of opioid dependency and chronic pain, and meperidine is not preferred due to its side effects and the availability of better alternatives. Therefore, for postoperative pain management in children, morphine by PCA is the most suitable option among the choices provided.