**Core Concept**
Acute onset of a cough, stridor, and dyspnea in a child is primarily due to upper airway obstruction, which can be caused by various conditions such as foreign body aspiration, epiglottitis, or croup. This condition can lead to respiratory distress and requires immediate medical attention.

**Why the Correct Answer is Right**
The correct answer is likely due to croup, which is a common cause of upper airway obstruction in children. Croup is characterized by inflammation of the larynx and trachea, leading to narrowing of the airway and stridor (a high-pitched sound on inhalation). This can cause a barking cough and difficulty in breathing. The symptoms of croup are often triggered by a viral infection, such as parainfluenza virus or respiratory syncytial virus (RSV).

**Why Each Wrong Option is Incorrect**
**Option A:** Foreign body aspiration is a possible cause of acute onset of a cough, stridor, and dyspnea in a child, but it is not the most common cause. Foreign body aspiration typically presents with sudden onset of coughing and choking, and may not always be accompanied by stridor.

**Option B:** Epiglottitis is a severe condition that can cause upper airway obstruction, but it is relatively rare and typically presents with severe throat pain, difficulty in swallowing, and high fever. Epiglottitis is more common in adults than in children.

**Option C:** Bronchiolitis is a common lower respiratory tract infection in infants, typically caused by RSV. While it can cause cough and dyspnea, it is less likely to cause stridor.

**Clinical Pearl / High-Yield Fact**
Croup is often referred to as "croupy" cough, which is characterized by a hoarse, barking sound. The symptoms of croup can worsen at night, and children with croup may require hospitalization if they are experiencing severe respiratory distress.

**Correct Answer:** C. Croup