There was a theory going around in the early days of Battlefront II that the game's campaign might had revealed Rey's parents were. While highly unlikely, the possibility that BFII protagonist Iden Jerso and his husband had mothered Rey was given plenty of encouragement, what with her husband being a skilled mechanic, pilot </i>and</i> Force Sensitive, and the couple having a child in Jakku about 20 years before The Force Awakens.
However, Battlefront II's latest single-player DLC "Ressurrection" reveals that the daughter wasn't Rey -- surprising no one -- but it does shed light on the backstory of another major character: Finn.
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The single-player campaign shows something called “Project Resurrection”, an initiative started by the First Order to train soldiers after the fall of the Empire. Without thousands of academy spread across the galaxy, the remnants needed a new source of manpower, and resorted to stealing children from impoverished planets on the Outer Rim and conditioning them to fight for them after years of intense training.
As seen with child soldiers in Africa, that kind of brutal treatment from an early age leaves sequelae, and the kids are often underdeveloped, aggressive, and blindly loyal to the faction that brainwashed them. It is straight from that environment that FN-2187 comes from when he is deployed as a stormtrooper at the beginning of The Force Awakens.
As everyone who watched the movie knows, even that brutal training wasn't enough to dull him to the horrors of war, and Finn soon defected the First Order and joined up with the Resistance (mercilessly killing hundreds of people in the process, because consistency is not important).
It should be noted that is not precisely new, as dialogue in Episode VII alludes to those very events. What Star Wars Battlefront II does is expand on it and in a way confirm it, giving us more backstory about the process which birthed one of the new trilogy's protagonists.
So there you go. While Rey was not the daughter of BFII's protagonist, Finn was the son of BFII's creepy child-stealing recruitment process.
