The two Muslim boys, aged 15 and 16, were charged with criminal conspiracy in connection with a terrorist enterprise and placed under court supervision, which will include educational measures, said a judicial source.
The pair, who are from the southern city of Toulouse, flew to Turkey on January 6th and crossed the border into Syria, apparently planning to join the thousands of foreigners fighting President Bashar al-Assad's forces.
According to Interior Minister Manuel Valls, as many as 700 French nationals may have joined the fighting in Syria, with perhaps one-fifth of them converts to Islam. About a dozen are believed to be minors.
French officials fear these radicals could be a ticking time bomb whose eventual return to France will pose a major security challenge in the future.
Investigators spent two days interrogating the two Toulouse teens after they were flown home earlier this week.
Their answers clearly show they succeeded in crossing the border into Syria, though the 15-year-old disputes travelling to a jihadist training camp, said a source close to the case.
A lawyer for the younger suspect called the charges "ridiculous" and said the boys' trip was for "humanitarian" reasons.
"The reasons for their trip had nothing to do with any terrorist enterprise," added a lawyer for the 16-year-old.
Nearly three years after it began, the war in Syria is increasingly drawing Islamist extremists to the region. Assad's regime has slapped the "terrorist" label on the entire opposition, but in fact the more moderate rebels are also fighting the extremists themselves.
French, British, Belgian and German officials have all voiced concerns about radicalised young Muslims from their countries heading to fight in Syria and returning home as battle-hardened veterans.