At least 46 children, some as young as 18 months, were raped near the village of Kavumu between 2013 and 2016.
Eighteen people, including a provincial lawmaker, went on trial in eastern Congo on Thursday for the rapes of dozens of children, victims' rights activists said.
At least 46 children, some as young as 18 months, were raped near the village of Kavumu between 2013 and 2016, sparking an international outcry and criticism of Democratic Republic of Congo's government for its slow response.
In June last year, authorities arrested Frederic Batumike, a deputy from South Kivu province, and members of a militia he is alleged to have led.
Rights groups hope the trial, which is expected to last several weeks, will strike a blow against impunity in Congo, where they say government forces and militia groups in the lawless eastern borderland have long used rape as a weapon of war.
The trial opened in a military court in Kavumu on Thursday with the defendants facing charges of rape, murder and organisation of an armed group, Jean Chrysostome Kijana, an activist representing the victims, told Reuters.
Proceedings began 10 hours late and lasted just 20 minutes, during which the defendants' names were read aloud.
"The start of the trial is a strong signal in the fight against impunity," said Kijana. However, he added that the delay to proceedings did raise fears that the trial could end up just being "yet another in a long list of botched trials".
Millions died in eastern Congo in regional wars between 1996 and 2003, most from hunger and disease. Dozens of armed groups continue to prey on local populations and exploit the area's rich natural resources.
Experts say Congo has made some progress in combating sexual violence and several high-level militia and army commanders have been successfully prosecuted in recent years, but the problem remains pervasive.
According to the government, Batumike's militia employed a spiritual adviser who told its fighters that raping very young children would confer supernatural protection.
Advocacy groups involved in the case say it has been particularly difficult to investigate because the victims are so young and their families were often asleep when the alleged rapes occurred.