One cannot enter the US on a B-2 visa for the purpose of adjusting status.
You really need to retain an experienced immigration lawyer, whether myself or one of my colleagues, to review all the facts, advise you, and handle the case.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.
I agree with Attorney Ferrari in that you cannot and should not even be thinking about using a B-2 for the express purpose of facilitating adjustment of status in the United States. The K-1/2 visa process can be frustrating. I wonder whether you've considered just filing an I-130 for your step-son now that you're married and once that's approved just having him go to the consulate abroad to obtain an immigrant visa as directed by the NVC? Feel free to contact me about this if you have additional questions.