Final answer:
The nurse should immediately wrap the client in a nearby blanket to smother the flames using the stop, drop, and roll technique.
Step-by-step explanation:
If a preschool-age client's clothing catches fire, the nurse should immediately wrap the client in a nearby blanket. This action is in accordance with the stop, drop, and roll technique, which is a standard safety procedure for extinguishing flames on a person's body. Wrapping the child will help to smother the flames and put out the fire as quickly and safely as possible. It is crucial that the nurse acts swiftly to prevent further injury or burns to the client.