There are projects that are trivial in Scratch that are hard in Racket, and vice versa. Porting your Scratch projects to Racket is not likely to be a very productive use of your time because they have such different strengths and weaknesses. I think your best bet is to pick some projects which are in Racket's world teachpack's "sweet spot" and work on those with your son.
Don't worry about trying to "replace" Scratch with Racket. My son is a fairly sophisticated Racketeer at this point but he still has loads of fun playing around with Scratch, using it for the things it is especially well-suited for and deeply enjoying its community aspects. There's nothing wrong with appreciating both.
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