As a parent in a country that mirrors Norway (minimal civilian armed response), my only thoughts are to drill / condition / hope that your kids respond promptly by running and hiding - I suspect when the full timeline of the attack is mapped out a lot of the kids stayed still and froze - pretty much a natural reaction.

For all sorts of crises, one of the major problems is people (not just kids) not recognising it and acting early.

Otherwise my thoughts go out to all victims and their families