Include my step-son to GC application

I recently got married, and my partner has a 12-year old son. I know I can include my spouse to GC application. But how about step-son?! What should I do to include him?

to glen.bennett840:

You should be able to include your step-son as he is only 12. As far as I know, if the kid is under 21 and unmarried, and your step-parent relationship was created before the kid turned 18, it should be fine.

to glen.bennett840:

What stage of GS are you in? If you haven't filed 485 yet, I think you'll be fine