I think the take-away from this is that SHAZAM =/= Kick-Ass + BIG.
They really should have casted a child to play Billy and spend a good 20 minutes showing how good of a person he is at such a young age. I want to see him going out of his way to help others even while he's dealing with personal issues that most kids aren't equipped to deal with. Maybe even witnessing things he wish he could help with but realizing he's too small. Like a woman being harassed or some teenagers beating up a nerdy teen.
Once he gets the powers we need a scene where he wakes up back at home and isn't sure if it even really happened until he witnesses another injustice he would otherwise be unable to prevent as a normal, powerless child. Then as he acts on his best intentions he remembers the magic word and proceeds to save the day. He is now a person with the heart to help people, and the tools as well.
Insert montage of him easily stopping robbers, natural disasters and alien threats.
Act 3 basically just needs to be SHAZAM: The Power of Hope. Because Billy is a kid, he understands kids, and his original power before he even met the Wizard was compassion. More than anything else, the movie needs to teach that compassion is the strongest power we will ever have, we just need to learn how to utilize it.