**Core Concept**
Bottle mouth syndrome, also known as baby bottle caries or early childhood caries, is a condition characterized by the rapid development of dental caries in infants and young children due to prolonged exposure to milk or other sugary substances from a bottle. This condition is often associated with the frequent and prolonged use of a bottle, particularly at night.

**Why the Correct Answer is Right**
The prolonged exposure of the teeth to milk or other sugary substances creates an acidic environment that fosters the growth of bacteria, such as Streptococcus mutans, which produce acid and lead to tooth decay. The frequent and prolonged use of a bottle, especially at night, allows for an extended period of exposure, increasing the risk of developing bottle mouth syndrome. The use of a pacifier, which is often used in conjunction with a bottle, can also contribute to the development of this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bottle mouth syndrome is not typically associated with thumb sucking.
**Option B:** This option is incorrect because while pacifier use can contribute to the development of bottle mouth syndrome, it is not the most frequent cause.
**Option C:** This option is incorrect because while bottle mouth syndrome can occur in children of any age, it is most frequently seen in infants and young children.

**Clinical Pearl / High-Yield Fact**
Bottle mouth syndrome is often referred to as a "milk-bottle caries" because of the role of milk in the development of this condition. To prevent bottle mouth syndrome, parents should encourage their children to drink from a cup by 12-18 months of age and avoid giving bottles at night.

**Correct Answer: D. Infants and young children.**