Freddie Freeman is Captain Marvel Junior. His super hero god body is that of a child the same age as he is, who is lame, literally, has to walk with a crutch, and CMJ's (A name he went by briefly as a Titan in the 90s.) uniform is identical to Captain Marvel, except that it is Blue instead of red. To transform into Captain Marvel Junior, he has to say the magic words "CAPTAIN MARVEL" which is the height of irony since while fighting evil he can't say his own name without retransforming into a 10 year old cripple kid.
Briefly between final crisis and flashpoint, Billy got to take over the Wizard Shazam's job guarding the Rock of Eternity.and Judd Winick wrote a book with Howard Porter about how the SHAZAM powers were put into play and Freddie had to earn those powers back while evil conspired to change the orientation of the universe from mostly good to mostly evil by undercutting freddie.
It wasn't an awful read.
His brother is Kid Eternity, also a Titan I believe, who has the power to bring forth any figure from history or fiction to help him in his adventures.