2003 Ford Windstar Won't restart after engin warm up if eng

This Windstar will not restart after starting and driving the car for any distance. Example: I start the car and drive to a store, shut the engine off and while the engine is still warm I try to restart the car and it won't start,,,,it acts as thoufh it is flooded. I wait till the egine cools (15 minutes to a half hour) and then it starts OK.
My wife also drives this car and I do not want this to happen to her. an you tell me what to replace to fix it??