As I said this rule was changed by USCIS on 2/23/2023, not DOS yet at that time, so the US Consulate might not understand this rule yet though it seems NVC accepted this rule for your case because NVC accepted the child's DS 260. The US Consulate and NVC are controlled by DOS, not USCIS.
That is why I suggest you consult or hire a lawyer to help you to justfiy your case based on the USCIS new rule which also applies to the child immigrant visa application through consular processing. Of course, you may ask the US Consulate to add the child first and if they don't add it, you can ask why and then, hire a lawyer later.
