The incident occurred on Saturday night, and was prompted by the sister's refusal to allow her brother to play with her Nintendo DS. Upset over this, the boy took a kitchen knife and stabbed her in the chest. The children's mother was awakened by the girl's screams and she was rushed to hospital, where she remains (although her condition is not listed as critical).
There are further reports from a follow-up story by Le Post of the boy citing "inspiration" from a Power Rangers game that involved throwing knives, and of the family suffering from a history of domestic violence at the hands of their estranged father." copypasta from Kotaku
I'm so glad that my sister was never into gaming when we were young. She'd have been all over my Game Boy and I'd have been all, "NO WAY!" Then BAM. Knifey knifey. Scary world innit?
edit: I'm sure someone will drop it in Off-Topic soon enough. Short attention span and multi-tasking.