Infections caused by viruses are common in childhood and adolescence. Most childhood viral infections are not serious but some of them are much more serious and can be life-threatening for children. The children’s immune system is not fully matured, and babies do not start producing antibodies until 6 months of age, which makes them vulnerable. There is a group of viral diseases that directly impact babies early in their lives, even being infected in utero (CMV, rubella, VZV, or parvovirus B19) and maternal disease threaten fetal development. Furthermore, some mild pediatric viral diseases may result in much more severe clinical presentation if an adult person becomes infected (mumps or measles). Despite the immunization efforts, childhood disease outbreaks are regularly identified, and reliable tests have a favorable impact on public healthcare.