Marchino61
Your comments made some sense before you came to this part of the paragraph:
you could even remind pax to help others first
That's exactly what you're
not supposed to do! (Another one who hasn't listened properly to the safety briefing
)
The simple point is this: if you're with children, they consume less oxygen (air) than adults. Therefore they can survive (however unpleasantly) whilst you fit your mask and check that it is working. If you fit the child's mask first and there is some problem, you are rapidly running out of air yourself, and you could both be in trouble, hence the briefing.
Next time
'listen and learn'