Kelly Rowland learned a lesson from Jon Voight ... don't talk about the biggest star in your life, and especially don't talk about their kids.

Kelly managed to say she's "ecstatic" over Bey's pregnancy announcement, but watch her dodge as our LAX photog asks if she, like pretty much everyone else, was in the dark.

She seems to motion she's having voice problems -- not sure if we buy it -- and then gives us a fist pump ... kind of like "Formation," right?