Child lock isn’t electronic, it’s a mechanica switch you can only access when the door is open that prevents you from opening the door from the inside of the car. Locking the doors does nothing, if the door is going to open it’ll automatically unlock if you pull the handle from the inside.

That's not how my old car (Mondeo 97) works.

I see in the US requirements that the rear side door lock has to disable both the exterior and interior handles. Odd.

Yes, but that was typically a difficult to access switch, not something you'd easily locate in a strange car. If the driver wanted to use the child lock, they'd just use it without telling the passengers (they would find out only after closing the door).

A difficult to access switch yeah, but then some cars required you to also lock that door from the inside to activate it.