How do I clean up the simple finder for a parental controlled account?
As you've confessed your developing skills, I'll just limit myself to tell you that, as far as I know, it's not possible to hide applications from a user that has Parental Controlled accounts, even with simple Finder. I believe Apple considered that it was too much trouble. 

What I'd do is move your son's applications to his /User/son/Applications and restrict access to /Applications for him. 

You may be wondering: "but wouldn't that mean I'd have to duplicate apps I also want to use?". And you'd be right.

:)