YOUTH by Isaac Asimov is a great sci-fi short story. Aliens, an explorer and a merchant, arrange to meet with an astronomer and an industrialist on Earth, after the wars which changed life as we know it. Unfortunately, the aliens crash land and are found by two children with plans of their own.
The misunderstanding between the six characters is very entertaining, but the ending is a fantastic shock. Just one more reason to love Asimov's storytelling.