Yes, I think you may take your kid with you and also bring her/his birth cirtificate and passport. A kid will make the interview atmosphere more comfortable, and
is also an evidence of you and your spouse's relationship.
I did the interview at Washington D.C. local office
last month and the officier actually even checked my daughter's passport
and birth certificate (she was born in US and not included in my I-485 application). Although I didn't get my passport stamped, but I do see the officer was very nice (maybe due to my kid was there).
Good luck!
Racoon
