Final answer:
To support the condition of nuchal rigidity in a 3-year-old child, vomiting would likely be the sign documented on the chart, as it is a common associated symptom and observable in a child who may not be able to communicate neck pain.
Step-by-step explanation:
A nurse is obtaining data from a 3-year-old child with nuchal rigidity. This term refers to a stiff neck, which is a well-known sign of conditions such as meningitis that affect the meninges of the brain and spinal cord. In the context of nuchal rigidity, particularly in a young child, the presence of neck pain would likely be difficult to assess due to the child's limited ability to communicate symptoms effectively. Instead, the nurse might document observable physical signs. Therefore, the sign most likely to be documented on the chart to support this condition in a 3-year-old would be vomiting. This is because vomiting, along with irritability, drowsiness, and sensitivity to light, can be associated with meningitis and other infections that might cause nuchal rigidity.