If he is your stepson, you basically cannot sponsor him (possibly some exceptions if adopted and you have custody / the mother passed away or similar).No son from my previous relationship 11 years ago before married
But if it's your natural son (by blood, therefore not your stepson, just your son), then he could be included as your dependent or sponsored later (but make sure to include as your non-accompanying child).
If you didn't include him in the previous sponsorship (that was rejected), you may have a serious issue and be unable to sponsor him. This is a question that you really should discuss with a lawyer because it does raise some serious and uncommon issues, that I doubt anyone here could answer.