ORLANDO, Fla. (AP) _ Prosecutors charged a 12-year-old boy with manslaughter in the shotgun slaying of his 7-year-old sister, although they said the shooting was an accident.

Prosecutor Danny Dawson said the boy, Marvin Williams, was grossly negligent in deliberately aiming a short-barreled shotgun that killed Calandra Graham.

''If at the time a gun goes off you've got control of the gun and you're pointing it at another individual, that crosses the threshold of culpable negligence,'' said Dawson.

Marvin's mother, Mattie Williams, said when told of the charge Wednesday: ''I don't understand it. But we will deal with it. We will deal with it.''

The two children were alone at home at the time of the Sept. 13 shooting, and the boy told investigators conflicting stories of what happened, said state attorney's spokesman Randy Means.

Investigators later determined that Marvin took the gun from an unlocked cabinet in his 18-year-old brother's bedroom and played with it for a few minutes around the house before returning to the bedroom to put it away.

When he saw his sister, Means said the boy pointed the gun and told her ''something to the effect of 'Don't worry, it's not dangerous.'''

The gun then went off, blasting the girl in the face.

Means said the boy's conduct was so careless that it rises to the level of culpable negligence, the standard used to prove manslaughter.

In a similar case in Orlando in June, 10-year-old Scott Feltner was shot and killed by 13-year-old Barry McDonald, who was not charged. But McDonald was not paying attention to where he was aiming the gun when it went off, Dawson said.

Means said prosecutors have not decided whether to charge Marvin Williams' 18-year-old brother, Efrem Bolden, with illegal possession of the shotgun used in the girl's death. A state law which took effect in October penalizes the owner of a weapon left where it can be easily obtained by children.