"A dew drop on a rose petal" is the classic description of a chickenpox rash.
Tiny fluid-filled vesicles form on pink spots from head to toe -- just like the description. It is usually preceded by a fever and becomes terribly itchy once the rash develops.
Fortunately, most children are vaccinated against chickenpox and the disease is becoming rare. It's possible to still develop the rash even if a child has been vaccinated, but the disease is mild in that instance and it's often difficult to recognize.