A judge on Monday ordered the girl to remain in juvenile custody on aggravated sexual assault charges.
The Dallas Morning News reports the family suspects the girl may have been molested years ago by a man her mother knows.
Dallas police say the 12-year-old allegedly told the two girls, who are 5 and 7, and boys, who are 4 and 5, that she would put them in a closet Saturday if they did not perform the sex acts.
One child later told a parent. The 12-year-old was arrested Sunday.
The five children were in the care of the current boyfriend of the 12-year-old's mother.