But as far as Shazam! 2 is concerned, it doesn’t sound like David F. Sandberg is concerned about all this since he’s willing to poke fun at the matter.
Still, while the comics have the luxury of playing loose with the passage of time, that’s significantly harder to do for live-action adaptations, so this was to be expected.
Eventually there will come a point where the members of the DCEU’s Shazam Family will have to be classified as adults; in fact, this is basically already the case for Grace Fulton’s Mary, as she was preparing to go to college in the first movie.