Warning: SPOILERS for Black Lightning's pilot episode ahead
Black Lightning premiered on The CW tonight, starring Cress Williams as the titular character - a mild-mannered high school principal by day, who uses his electricity-based powers to defend the city from criminals at night. The show joins an already busy slate of superhero shows on the network, with this week also seeing the midseason return of Supergirl, The Flash, and Arrow. And much like his fellow CW crime-fighters, Jefferson Pierce has a terrible superhero disguise that inexplicably makes him unrecognizable to his own family.
In fact, for much of the episode Jefferson doesn't even bother to wear a disguise. He takes down two police officers who corner him in an alley, wearing simply a suit and bow tie, but shows no concern that they might be able to identify him later on. This may well be part of the show's commentary on racism (earlier in the episode, Jefferson is pulled over by two other cops because of his "resemblance" to a wanted thief), but that doesn't explain why his own daughters are unable to tell that Black Lightning is the man who raised them, when he's standing just two feet away.
This is a common, long-mocked trope in the superhero genre, and J efferson isn't even the worst offender on The CW. When Arrow first began, Oliver Queen was able to create an impenetrable disguise simply by wearing a hood and some green eyeshadow (he later graduated to the more traditional domino mask). The Flash disguises his face and voice by vibrating at a high speed, but it still requires some suspension of disbelief when his family and friends are able to talk to him at length without recognizing him. And as for Supergirl - like her cousin, she doesn't bother to cover her face at all (the show attempted to explain this, via James Olsen, by saying that no one recognizes superheroes in street clothing because "the world can’t believe that there’s really a hero in their midst").
In a way, Black Lightning's disguise being comically terrible makes him a firm part of the CW family (though the official word is that it's not set in the Arrowverse), and at this point family members not seeing through terrible (or non-existent) disguises is more of an amusing quirk than an actual plot hole. However, it does undermine Black Lightning's slightly more serious tone when Jefferson goes to rescue his two daughters from the clutches of the 100 Gang, and they fail to recognize him as their father just because he's wearing a pair of goggles.
The in-universe explanation for how Jefferson gets away with such a poor disguise appears to be that every time Black Lightning shows up, he uses his powers to take out the lights, presumably along with any security cameras that might be in the area. As for his family - well, it won't be too long before his daughters become superheroes themselves, at which point it won't matter how bad his disguise is.