If your child is ill, it means he's strengthening his immunity. Germs, bacteria and viruses are naturally present in our environment. When your child is exposed to them, his defenses may not always protect him. Once inside, these germs quickly find a home inside the cells of your child's body, where they take over and use the cells to make more germs. However, during all this, your child's body is not just standing idly; it has an immune system that is attempting to fight off the infection by sending in an army of chemicals, antibodies and blood cells. Unfortunately, the battle itself can make your child feel sick, while some of the body's defensive chemicals can cause unpleasant symptoms such as fever. The amazing thing about the immune system is that it has a memory. Once it has seen and fought a germ, it remembers it and can mount a much larger response the next time the germ visits. Often killing the germ before it can establish itself and cause illness. This is called 'immunity' and it is also the basis of all the vaccines that you give to your child to help prevent serious diseases. The thing about illness and children, particularly younger children, is that they haven't been around for very long and their bodies have not met many of the germs that surround us. Therefore, they get sick often. This leads to an important fact – when children get sick, they build immunity.