I think the crying child was the customer’s child.
Notice, even with all the commotion, the young man does not get the child out of that snake pit with chairs and curse words a-flying. Instead, he hold the child near a table and kind of waits around. Maybe that was her brother or some fellow who is used to seeing the girl act up while in public.
Checking through the video again, the man and child appear to have come from the counter, and I am assuming they gave their order and took a seat until their number was called. They sat away from Miss lovely who was already seated and yelling insults at big girl. I don’t think the man and boy were connected with Miss lovely.