War of the Buttons.

A village in the South of France, 1960. A band of country boys aged 7 to 14, led by fearless young Lebrac, wages an uncompromising battle against their sworn rivals, the kids from the neighboring village. A war of honor and allegiance that's been kept alive for generations, in which humiliation is the most fearsome defeat and no tactic is too extreme, including attacking the enemy stark naked!