In a relatively similar vein, there was an article about the police planting a wallet with money in it in the New York subway. Unsuspecting victims would pick up thewallet, take it with them, then get arrested for theft by the NYPD. Obviously there was a shortage of crime in the metropolitain area.
The logic was - to avoid theft charges, you must turn over found material as expeditiously as possible. There’s a manned ticket booth somewhere in the station. Telling the police “That was my train. I was planning to turn it in where I exit the subway…” was not good enough. The police wrote a summons and said “Tell it to the judge”.
In a similar vein, a friend who worked in Saudi Arabia for several years repeated the old story that if you lose your wallet, it will be right where you dropped it two days later, because an honest citizen would be terrified to touch it for fear of being charged by police as a thief (not a good thing in Arabia).
So to the OP’s question… where does North America stand on moving someone’s kid? Well, you better have demonstrated definite intent to take the child directly to help, especially if male(gay or straight). You better be prepared to explain why you could not call for help, ask a passerby to call for help, did you head directly for the nearest open building likely to have a phone (like a store), etc.
You quickly would learn why corporate lawyer think like they do - whether you are charged or not, if someone even thought there was question what was going on… if you did not spend a fortune on legal defense, at the least you would end up on the local watch list, maybe be added to a mug shot book, and be interviewed every time there was an “incident”.
As for the “drunk mom” question… In many jurisdictions, child care professionals, teachers, doctors, etc. are OBLIGED to report incidents of child abuse. Therefore, at the very least you are obliged to call the authorities.