I was in the Brownies as a child. 
Yeah, but that's more about making certain you've got clean knickers on in case you have an accident, isn't it? -I was in the Guides but I was threatened with demotion because I couldn't remember the pledge!!!- I certainly have no recall of them telling us to be on our guard because certain people couldn't be trusted. Like others, I've discovered that it's a fact of life, but I'm damned if I'm going to let them spoil my pleasure in the many, MANY of my knowledge who CAN be trusted. Perhaps it's down to good luck, but I've met only a small handful who've proved to be less than trustworthy.