The pair, aged 15 and 16, were both given six-month suspended sentences, a sign that the court did not wish to "stigmatise them as terrorists", according to one of their lawyers, Agnès Dufétel-Cordier, who had called for acquittal.
They left Toulouse for Syria on 6 January 2014, one of them having asked his mother for 500 euros for a supposed school trip to Spain.
He left her a letter telling her to "imagine that I am dead and get on with your life normally".
They returned to France on 25 and 27 January after having been collected by their parents.
In a behind-closed-doors session they told the judge that they had not intended to fight jihad but to join the Western-backed Free Syrian Army to fight Syrian President Bashar al-Assad.
Investigators found that they joined a brigade led by Mourad Farès, one of France's main internet jihadi recruiters who was arrested in Turkey and handed over to France in 2014.
One of the youths admitted having taken part in "surveillance missions" but denied handling weapons, the other said he had carried out guard duty armed with a Kalashnikov.
They said they left Syria because of the "rotten atmosphere" among French-speaking fighters.
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