A 10-year-old girl was sleeping at home in Hayward in the US state of California at about 2am on Thursday when shots fired outside her house hit her in the buttocks.
She then complained to her parents about the pain, the Daily Mail reported.
But the girl's mother and sister examined her and believed the blood was from her starting her menstrual cycle.
The victim was given a pad to use and told to go back to bed, said the police. The girl's father, 42, said that he heard the shots, but thought they sounded like bulbs popping.
The family lives in a neighbourhood known for gang activity.
A car parked outside the home was hit by some of the bullets.
The girl's 15-year-old sister called 911 the next morning after they realised that the pain in her pelvic region was due to a bullet.
Emergency responders were dispatched at about 7.30am, said the report. The girl went into surgery on Friday to remove the bullet.She was last reported recovering in hospital.
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