## Core Concept
The management of postoperative pain in infants, especially those as young as two months old, requires careful consideration of their physiological and developmental stage. Infants have a unique response to pain and analgesic medications due to their immature liver and kidney function, as well as the blood-brain barrier. Effective pain management in this age group is crucial to prevent distress, promote recovery, and reduce the risk of long-term consequences.

## Why the Correct Answer is Right
The correct approach to postoperative pain relief in a two-month-old infant involves the use of **acetaminophen (paracetamol)**. Acetaminophen is widely recommended for its analgesic and antipyretic properties, with a relatively favorable safety profile in infants when used at recommended doses. It is primarily metabolized in the liver and excreted by the kidneys, and its pharmacokinetics are well understood in pediatric populations. The American Academy of Pediatrics and other guidelines often suggest acetaminophen as a first-line agent for mild to moderate pain in infants.

## Why Each Wrong Option is Incorrect
- **Option A:** Although opioids are potent analgesics, their use in infants requires caution due to the risk of respiratory depression, and they are generally reserved for severe pain. Monitoring for respiratory depression is critical, making them less ideal for routine postoperative pain management in this age group without close monitoring.
- **Option B:** Ibuprofen, an NSAID, can be used in infants for pain relief but is typically recommended for infants older than 3 months due to concerns about renal function and potential effects on the developing kidneys. It's not the first choice for a two-month-old infant.
- **Option D:** Muscle relaxants are not typically used for pain relief but rather for their effect on muscle tone. They do not address the underlying pain and can have significant side effects.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **dosage and administration of acetaminophen in infants must be based on their weight**, and it's crucial to use a formulation suitable for infants to avoid overdose. The standard dose of acetaminophen in infants is 10-15 mg/kg per dose, with a maximum of 60 mg/kg per day.

## Correct Answer: C.