I'm going to give my son money without telling my wife.
Why would you give your son money without telling your wife? It doesn't sound that good.
I don't want her to know that I'm helping him financially.
I understand that you want to help your son, but hiding this from your wife is wrong. She should know what is happening since she is his mother and decisions like this should be made together. The two of you should discuss this and come to an agreement about how you can handle the situation.
It's is good enough that I help him with his homework and I'm a good dad already.
Yeah you are a good daddy but doesn't mean you should hide things behind your wife. Telling her what you are doing doesn't take any credit away from you. It's better off to avoid surprises especially when your wife finds out on her own.