Not a great book about stranger danger in the least.
First of all, while the topic is important, what it doesn't do, is reassure a child that there's safety in the world anywhere at all except perhaps behind the closed doors of their own home. Which sadly isn't always the case. Sister sees danger around every corner after the well-meaning lecture that Papa Bear gives her, but then doesn't give her any way to build her confidence back. Instead we're leaving the child scared of the world, and thinking twice about going outside.
Where is the mention of the "safe" adults - finding a policeman for example when feeling threatened. Or in going to another trusted adult when safety is compromised (talking to a teacher, or parent, or other person in authority). Children need to be careful about stranger, and the threats they pose, but sadly, the majority of those who will be harmed, are harmed by someone they know. They need to be taught to instead trust their instincts - that when something feels 'wrong' it's ok to go and talk to a TRUSTED adult about the situation. Or even that there are safe places and safe people in the world.
This whole book says too much, and at the same time, doesn't teach enough. If that makes sense. Definitely a poor choice to help a child to understand why it's not OK to be friendly with every person they meet.