As your baby’s immune system develops, understanding how it can be compromised is important to ensuring better lifelong health. Infectious diseases are those that happen when organisms, like viruses, bacteria, parasites or fungi get into the child’s body. These types of illnesses can pass from one person to another person, making it important to be aware of them. We care for children with a wide range of illnesses, especially those that develop when a child’s natural defense system is weak.