## Core Concept
The production of immunoglobulins, specifically IgG, is a crucial aspect of the immune system's development. IgG is the most abundant type of antibody found in blood circulation. The ability to produce IgG starts early in life as part of the maturation of the immune system.

## Why the Correct Answer is Right
The correct answer, **6 months**, reflects the age at which infants begin to produce IgG antibodies effectively. This is because, initially, infants are protected by maternal IgG antibodies transferred through the placenta and breast milk. However, as this protection wanes, usually around 6 months of age, the infant's immune system starts to produce its own IgG in response to environmental antigens.

## Why Each Wrong Option is Incorrect
- **Option A: 3 months** - This is too early for an infant's immune system to start producing significant amounts of IgG on its own, as they are still largely protected by maternal antibodies.
- **Option B: 12 months** - This is too late, as the infant's immune system would have already begun producing IgG by this age.
- **Option D: 18 months** - Similarly, this is too late for the onset of IgG production.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the infant's immune system matures gradually. By around **6 months**, infants typically start to produce IgG antibodies in response to infections or vaccinations, marking a significant milestone in immune system development. This timeline can influence vaccination strategies and the management of infections in infants.

## Correct Answer: C. 6 months