According to investigators, while the grandmother of the boys was in the bathroom, the 4 year-old retrieved a knife from the kitchen and subsequently stuck the knife into the back of the 12 year-old.
The 12 year-old sustained a single non-life threatening wound to the back, police aid.
He was transported to Beth Israel Hospital for treatment.
No charges were filed in the case.
Police do not know what led to the stabbing.
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