she's about six. She comes round with annoying frequency to play with my nearly 12 yr old. My 10yr old does not acknowledge her in any way but my eldest is far kinder to small children 
Anyway, they were in the bedroom and my son came down in floods of tears. She, according to him, had no allowed him to play with the toy they were playing with and had said "fuck you."
She appeared and I got my keys and said "you need to go home. Now."
I then said to my son. "Whst happened?" and he told me, again.
She said "I didn't."
I don't believe her.
I said "Just go home."
And my son yelled "And never come back"
She left.
Should I have done it differently?
I then had to spend ages trying to sort out my son who was yelling that he wanted her to die.
(In case this seems somewhat extreme, it is probably important to know that my boys both have autism)
The girl is quite likely to try to come and play again at some point. Do I tell her to never come again, tell her mother to not let her come round again or try to convince my son to forgive her?