What are 5 different common childhood diseases?

Classic 5 exanthema. Chicken pox, measles, rubella, mumps, roseola are the classic "childhood diseases" traditionally spoken of by lay people. They are in reality viral illnesses that have a rash associated with their clinical presentation.
Too broad. Quite frankly, this question is too broad. Are you talking about infectios, cancers, allergies or what? You need to be much more specific.