**Core Concept**
Neonates and young children are prone to bacterial meningitis, primarily caused by encapsulated organisms like *Streptococcus pneumoniae*, *Neisseria meningitidis*, and *Haemophilus influenzae*. The immune system of this age group is still developing, making them more susceptible to infections.

**Why the Correct Answer is Right**
In a 1-year-old child, the most common cause of bacterial meningitis is *Haemophilus influenzae* type b (Hib). This is due to the child's immature immune system and the fact that Hib is a highly virulent organism that can easily colonize the nasopharynx and spread to the central nervous system. Hib meningitis is often characterized by a rapid onset of symptoms, including fever, seizures, and altered mental status.

**Why Each Wrong Option is Incorrect**
* **Option A:** While *Streptococcus pneumoniae* is a common cause of bacterial meningitis, it is more commonly seen in older children and adults. In young children, Hib is a more common cause.
* **Option B:** *Neisseria meningitidis* is a common cause of meningitis, but it is more commonly seen in teenagers and young adults. In young children, Hib is a more common cause.
* **Option D:** *Escherichia coli* is a rare cause of bacterial meningitis in children under 1 year of age.

**Clinical Pearl / High-Yield Fact**
In young children, the presentation of bacterial meningitis can be subtle, with non-specific symptoms such as irritability, vomiting, and refusal to feed. A high index of suspicion is essential for early diagnosis and prompt treatment.

**Correct Answer:** C. *Haemophilus influenzae*