Freddy Freeman is a foster child at the same home Billy Batson is placed in the movie. He is a bit of a wiseacre and walks with a crutch. When Billy receives the wizard's power Freddy is the one who helps him learn how to use it.
In the comics Freddy Freeman became "Captain Marvel Jr." as discussed in my post of the DCUC version. At the end of the Shazam! film (spoiler alert) Billy shares his power with the rest of his family and they all turn into Marvels without names. Freddy basically has a blue version of Billy's suit much like in the comics but his cape remains white.