C. Headaches and vomiting.
The most common clinical manifestations of brain tumors in children are headaches and vomiting. This is because the tumor can cause an increase in intracranial pressure, which can lead to these symptoms. Seizures may also occur, but they are less common than headaches and vomiting. Irritability is a non-specific symptom that can occur with many different conditions and is not specific to brain tumors. Fever and poor fine motor control are also not common symptoms of brain tumors in children.