Billy Batson's life before he met the wizard Shazam is known briefly from the pages of Whiz comics #2 where we are told the origin of how Billy was given the power to become Captain Marvel. But we don't know what Billy's life was truly like. However, Captain Marvel Adventures #88 sheds some additional light on Billy's life that we didn't know before! To some degree, you can consider Captain Marvel Adventures #88 as the prequel to Whiz comics #2.
In Captain Marvel Adventures #88 we have "Captain Marvel in Billy Batson's Boyhood!" We find Billy gathering some old clothes to give to charity and he reminisces about his life before he met the wizard Shazam years earlier. What was life like for the young orphan while he lived with his Uncle Ebenezer? It was a life of tremendous hardship.
Uncle Ebenezer was a cruel man, and he tried to make Billy steal for him. Billy wouldn't steal and instead stood for hours in the cold selling pencils, trying to make money for his uncle. His uncle beat him and barely fed him regardless of how much money Billy was able to earn. Billy's clothes were patched, his shoes had holes in them, and he has no proper winter clothing. Billy was truly living in a desperate situation.
One day, Ebenezer and Billy receive the news that a distant relative of Billy's has died and left Billy with a large sum of money. Ebenezer says he knows exactly how to put the money to good use, and that won't include new shoes for Billy. Ebenezer throws Billy out into the snow for Billy's ungratefulness for not appreciating the care Ebenezer provides him!
Luckily for Billy, a police officer finds him half-frozen sleeping on a park bench covered in snow. The policeman takes him to the hospital where Billy is treated with a kindness that he has never known. The nurse tells him to eat up as he is half-starved from the horrible care received from Ebenezer.
By the time Billy is fully recovered, winter is over and it appears to be spring time (notice the snow is gone). Billy returns to the home of Uncle Ebenezer only to find that it's been abandoned! A neighbor tells Billy that Ebenezer left right after he came into a good bit of money!
It's at this point that Billy's boyhood story in Captain Marvel Adventures #88 ends. I'm assuming that when Billy returned to an empty home - a home his uncle had kicked him out of - that is when Billy took on the job selling newspapers and sleeping in the Fawcett City subway as described in the pages of Whiz comics #2.
I have to admit that there are some inconsistencies between Whiz comics #2 and Captain Marvel Adventures #88. Whiz #2 says Uncle Ebenezer stole the money and bonds given to him from his father, but Captain Marvel Adventures #88 (CMA #88) says that Billy came into a good sum of money from a distant relative. Here are two possible ways to reconcile these differences. The first possibility is it could be Uncle Ebenezer had already taken Billy's inheritance from his father (as mentioned in Whiz comics #2) but is living a miserly life in a ramshackle house. When he gets the additional money from Billy's distant relative in CMA #88, he kicks Billy out. The second possibility is that the money from Billy's distant relative in CMA #88 is actually the money Billy's father left to him (Whiz #2) and Uncle Ebenezer lies to Billy, saying the money is from a 'distant relative'. I think both of these offer a plausible explanation for the slight inconsistencies between Whiz comics #2 and Captain Marvel Adventures #88.
To say Billy Batson had a hard life is an understatement. He was an orphan, beaten and betrayed by his Uncle Ebenezer. He had already lost his parents, and he almost lost his life from the neglect of his uncle. For many people, that would be a convenient reason to turn your back on kindness and allow yourself to be embittered and broken. How many people could recover from so many devastating blows? Billy's young life was truly tragic, but that tragedy never corrupted his heart. It is for these reasons we see Billy as a true hero and role model. Billy never lost his good heart and positive outlook, and those are the things the wizard Shazam saw in him that made him his choice to become Captain Marvel, the World's Mightiest Mortal.