http://www.russiatoday.com/news/news/36941
Zhenya was seven.
The little girl says the man held a knife to her throat, and demanded that her brother bring him all the money he could find. Zhenya did as he was told. But when the man started undressing his sister it was more than the boy could bear.
Zhenya seized a knife from the kitchen and plunged it into the man's back. This didn't kill the attacker, but it was enough to set Zhenya's sister free. She ran for help. But it was too late for her brother - he was stabbed eight times.
Zhenya was seven.