Tourist woman and girl

Does anyone know who played each of the four family members who stop at the gas station where David is calling his home toward the end of the film (the one with the Bait and Worms sign) so that the mother of the family can use the rest room? The credits listed on here mention only the father and son. What kind of gag is that? I don't like to sound unreasonable but how does this make any sense at all? It's as though we're expected to look toward the notion that the mother and daughter weren't even played by real people but rather were just painted on the screen by some kind of special effect! I've seen tons of things in movie credits that don't make sense but how is this one to be explained?

Long live the 80's!