Wasn't there a story from the life of Mohamed, where a man asked him whether he should tie up his camel while he went to pray, or whether he should leave it to Allah's will?

Mohamed said to tie up the camel.

Sorry if I've garbled the story for people who know it better, but it indicates that you should take obvious precautions before you rely on Allah to help you out. I'm no religious expert, but it seems probable that the advice might be applied to strapping your kids into your 4WD, and helping an injured man.