First, get your legal relationship to the child correct in your mind. For immigration purposes, he is simply your stepson.
Even without the guide, the I-130 instructions spell out clearly what is required for spouse and what is required for a stepchild. You will be submitting evidence of your bona fide relationship to your wife, but nothing like that for the stepson. For him, you are simply providing evidence you are married to his mother and that he is his mother's child. Presumably, he will travel with his mother. Whether you are traveling with them or not, is irrelevant.