Alternatively, pneumonia-causing bacteria can invade the lungs (pneumococcus, streptococcus, staphylococcus, Haemophilus influenzae). Other childhood viral infections such as chickenpox, measles, rubella, herpes, and mono can cause pneumonia directly. Viral pneumonias are fairly common. They peak during the toddler years, and become a bit less common each year. Bacterial pneumonias are less common. Most occur in children with cystic fibrosis or an underlying immune problem. All children who get two or more pneumonias within one year should have their immune system and lung anatomy evaluated by their doctor, to ensure they have no underlying illness putting them at greater risk for pneumonias. What are the symptoms?