**Core Concept**
Zinc supplementation is essential in infants and children to prevent zinc deficiency, which can lead to growth retardation, impaired immune function, and increased susceptibility to infections.

**Why the Correct Answer is Right**
Zinc plays a crucial role in various physiological processes, including DNA synthesis, protein synthesis, and immune function. In infants, zinc deficiency can occur due to inadequate dietary intake, increased requirements for growth, and poor absorption from breast milk or formula. Supplementing zinc in infants helps bridge this gap and ensures optimal growth and development. The recommended dose of zinc for infants is 2-3 mg/day, which can be achieved through supplementation or fortified foods.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not provide any information on zinc supplementation, making it an incorrect choice.
**Option B:** There is no specific contraindication for zinc supplementation in 12-month-old babies; however, excessive zinc intake can cause gastrointestinal side effects.
**Option C:** Zinc supplementation is not contraindicated in infants with diarrhea; in fact, zinc supplementation has been shown to reduce the duration and severity of diarrhea in children.
**Option D:** This option is incomplete and does not provide any relevant information on zinc supplementation in infants.

**Clinical Pearl / High-Yield Fact**
Zinc deficiency can manifest as growth retardation, hair loss, and impaired wound healing in infants and children. Clinicians should consider zinc supplementation in infants with these symptoms or those at high risk of zinc deficiency.

**Correct Answer: D.**