"Thursday marks the first step in a process to determine whether Lubanga is guilty of the war crime of conscripting children under the age of 15 and using them to participate actively in hostilities," ICC deputy prosecutor Fatou Bensouda told a press conference.
"Regardless of the outcome of the proceedings, this case will expose the destructiveness of forcing children to fight adult wars," she added.
The prosecution has charged Lubanga, 45, with three counts of war crimes.
They say that he commandeered children as young as ten to fight for the armed wing of his Union of Congolese Patriots (UPC) during the wars that ravaged the Democratic Republic of Congo (DRC).
The UPC militia, known as the Patriotic Forces for the Liberation of Congo (FPLC), mostly consisted of ethnic Hema and fought against ethnic Lendu forces in the northeastern Ituri region of the vast country.
The DRC is among nations with the largest number of child soldiers in the world, Bensouda said. At the height of the war as many as 30,000 children were associated with armed groups.
Lubanga, the ICC's first suspect in custody, has been named in connection with a long series of human rights abuses in the Ituri region, where fighting over gold mines and other resources has claimed more than 60,000 lives since 1999, according to humanitarian groups. He has denied all accusations against him.
In a document outlining the charges against Lubanga released Thursday the prosecution gives the example of a 13-year-old girl, whose name has not been released, who was abducted in August by the armed wing of the UPC and forced to participate in several attacks.
During the child's time in the training camp, Lubanga visited, the prosecution said, to address the troops.
"Whilst encouraging them, they (Lubanga and his deputy) also threatened that they would be killed of they attempted to flee the camp," the document reads.
The child soldiers were later instructed "to kill all Lendu including men, women and children", the prosecution said.
On Wednesday, defence counsel Jean Flamme said the charges and the evidence against his client were "often lies". The Belgian lawyer cast Lubanga as a politician and a man committed to peace.
According to the defence the case against Lubanga is a political prosecution supported by members of the international community who wanted to get rid of him because he opposed giving out mineral concessions in Ituri to foreign companies.
Thursday is the first day of a 12-day confirmation hearing set to run through to November 28.
During the sessions, the prosecutors will present the charges against Lubanga and his defence will have the opportunity to contest them. Finally it will be up to the judges to determine whether there is enough evidence to support the charges and proceed to trial.
Prosecutors will present an overview of the evidence, including written testimony from six former child soldiers. There will also be one witness testifying in court but she is not a former child soldier, the prosecution said Wednesday.
The defence will then present evidence to contest the charges. The judges will also hear submissions from lawyers representing victims from the DRC.
The hearing is scheduled to close on November 28. The panel of three judges, presided by French judge Claude Jorda who was formerly on the bench of the International Criminal Tribunal for the former Yugoslavia, will then have until late January to decide if there is enough evidence to warrant a trial.
If they rule there is not enough evidence Lubanga could go free but prosecutors could also file new different charges against him which would then have to be considered in another confirmation hearing.