Blac Chyna's Six Flags stroller freak-out started when some kid touched her baby girl -- and all hell broke loose when one phrase was uttered in her direction ... "hood rat."
Sources close to the situation tell TMZ that the girl who made contact with baby Dream began shouting at Chyna shortly afterward, calling her the derogatory term. That girl began inching closer to Chyna as well, causing BC's entourage to step in to block Chyna.
We're told the instigating girl ended up pushing one of Chyna's friends, and a fistfight broke out. Meanwhile, Dream and King were both whisked away by their nanny before all the mayhem.
As we reported ... Chyna addressed the public meltdown by saying she was simply defending her daughter, and expressed she would protect her children "at all costs."
While it would seem that Dream's safety would be enough to set Chyna off, it appears that the final trigger was the term "hood rat."