Low Zinc levels are associated with an increased risk of infection in small children. This is because children have a less developed digestive tract when compared to adults. Therefore, zinc absorption via dietary means is not quite as sufficient. This, intuitively, leads to lower zinc levels in children as compared to that of adults. This effect is more noticeable in low income/underdeveloped countries 

Research suggests that zinc supplementation would be beneficial for children in this case to help prevent bacteria infection. This would in turn lead to lower rates of pneumonia in children, especially those in underdeveloped regions. This area of research is important because pneumonia is responsible for a large proportion of disease incidence and death in young children.  

Source: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD005978.pub3/abstract;jsessionid=A54AA3C4FAAB5DBEC85DF25BF5178202.f04t03

Contributors 

Gage Winger, Mary West, Troy Watson Katie Weisshappel