The shooting happened in the 3100-block of West Fillmore Street on Valentine's Day, shortly before 8 p.m. Police said the two siblings somehow gained access to a gun in the home. The girl was handling the weapon when it went off, striking her brother in the neck.
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He was taken to Stroger Hospital in serious condition.
Lucreshia Curtis is now charged with two misdemeanor counts of child endangerment, Chicago police said. She was arrested on Saturday night and is due back in court on March 20.
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The boy was one of 11 kids wounded in shootings across Chicago that weekend.
The Sun-Times Media Wire contributed to this report.