Honestly, maybe you think you were saying that in a "funny" way because you call him "Bro". But this is an online forum, and we can only judge your tone by your words, not by your facial expression, your intonation, your gestures, etc.
Looking only at the words, you are not very appretiative of his efforts to help you.
For your case, I do think an embassy or 國內的出入境事務管理局 can provide you with the best answer.
If I remember it correctly, once you becomes a citizen or green card holder, by chinese laws, your child is not Chinese citizen anymore (it looks like China does not care whether the new country admits citizenship by birth). If I were you, I would be worried more about his passport being tore up at the chinese customs.
If you only want to prove your relationship, a birth certificate should be OK. But again, I am not sure. If only one of the parents accompanies the child, you need another parent's signed and certified agreement.
Again, ask your embassy...
