AOS of stepchild in US who attends interview?

[dm559 34]

Hi, my stepson is adjusting status here in the US (under 21)and we just got a notice which says "Request for applicant to appear for initial interview" and then it gives a list of what appears to be general stuff to bring to the interview. Documents which we already submitted with I-130 and I-485. My question is, do I (petitioner, American Citizen) am I supposed to attend the interview or just my stepson? The notice just says that if it's marriage based then the spouse has to attend, which he's not married. Also what happens at these interviews? The email notification said that it was test/interview but this notice is just initial interview. Thanks in advance.

(Side note)

(My wife is also immigrating to the US but she miscarried our child so her immigration was delayed while she recovered. This caused our son's immigration to advance further than hers. Originally we were going to live abroad and my stepson came to the US with me while I prepared for the move. Our son fell in love with the city I was living and really wanted to attend college here so my wife and I decided to move to the US instead.)