I agree that it is head vs heart and in a lot of cases it is doubtless that parents will help children first.

There is no reason why you cannot hold your breath at altitude, however, you have to recognise the situation you are in first and take a breath before the decompression occurs. In the case of an explosive decompression air will be forcibly expelled from you by the nature of the situation - higher pressure inside you, lower pressure outside. This will lead to other gas expansions inside the body that can cause problems - in the ears and sinuses, in the upper and lower intestinal tract sometimes even in your teeth. If you have been diving, and in some people even if they haven't been diving, you may start to suffer from the bends.

A rapid decompression is a nasty thing if you are prepared for it, if you are dozing or watching a movie it would come as a huge shock. So would the flight path of the aircraft immediately after the decompression. It is not like the movie's where the aircraft plummets out of control, but the pilots will carry out an Emergency Descent, which will be far more violent than anything a normal passenger will ever encounter, it may feel like an out of control plummet.