Maybe briefings could be reworded ("pull the oxygen mask so that at least X feet of tube is visible" might be helpful). Right now the instructions seem to be "pull this thing an unspecified amount - there's no way to tell whether you pulled it enough except that you'll become unconscious and may die if you didn't (thanks for making my point, D Guerrero!) - if you pull it too hard you may break it" All this is to be done while many people are panicking. Subsequent irrational upset is not surprising and might be reduced with a little rewording.
"It is the action of pulling the mask towards your face that opens the supply of oxygen"......is that piece of information not clear enough?
It matters NOT what any safety card says about placing the 50% mix of oxygen and cabin air?? over your face first, any parent would tend to their child first NO MATTER WHAT..
Responsible parents would surely follow the correct procedures as covered in the briefing - this is why it is mentioned. A parent cannot attend to their children if they are unconscious!