Final answer:
The nurse should use standard precautions and isolate the preschool child with chickenpox in a private room to prevent the spread of infection to other patients.
Step-by-step explanation:
If a preschool child is diagnosed with chickenpox (varicella) while hospitalized, the appropriate nursing action to ensure safety for all children on the unit is c) to use standard precautions and isolate the child in a private room. Isolation in a negative-pressure room is not typically required for chickenpox. Administering antiviral medications to all children on the unit is not necessary and may expose them to unnecessary side effects. It is not advisable to allow the child to interact freely with other children since chickenpox is in fact highly contagious, especially to those who have never been infected or vaccinated.
Following standard precautions includes strictly adhering to hand hygiene and using personal protective equipment when necessary. Isolating the child in a private room helps to prevent the spread of infection to other vulnerable patients as the varicella-zoster virus can spread through direct contact or inhalation of particles from the skin lesions.