**Core Concept:** Oral thrush is a fungal infection caused by the Candida species, specifically Candida albicans. It commonly affects infants due to their immature immune systems and the presence of specific risk factors.

**Why the Correct Answer is Right:** In this question, we are looking at the age group at which oral thrush develops most commonly in infants. Candidal infections primarily occur in infants due to the immature immune systems that are unable to effectively combat the Candida albicans fungus. Additionally, infants are exposed to risk factors like breastfeeding, poor oral hygiene, and the use of antibiotics, which can disrupt the normal oral flora and promote fungal growth.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because oral thrush is more likely to develop in infants, not older children or adults.

B. Although oral thrush can occur in premature infants, this option is too specific and does not cover the broader age group of infants.

C. While oral thrush might affect newborns, this option is too narrow and does not consider the broader range of infants.

D. While breastfed infants are at higher risk, this option is too specific and does not encompass the broader age group of infants.

**Why the Correct Answer is Right:** The correct answer, "infants," covers the broad age group that is most susceptible to oral thrush. In this age group, the combination of immature immune systems and risk factors increases the likelihood of developing oral thrush.

**Clinical Pearl:** Breastfeeding and antibiotic use are key risk factors for oral thrush in infants, which can lead to oral thrush symptoms such as white patches in the mouth, difficulty feeding, and irritability. Monitoring infants for these signs and promptly treating infections can help prevent complications and improve outcomes.