How do i teach my puppies not to follow strangers?

I have 3 month old puppies and they've recently began to explore the world and the thing is they follow their mom outside the yard and when they are outside they play with strangers, ok i know its good to have a socially mannered but not were I live. Here they steal puppies they poison dogs and I dont want that to happen to them or get runover by a car. Their father was quite the coward and explorer their mom was also a coward and an explorer but recently since she gave birth she's become more vicious and that is what i want, how do i prevent them from becoming cowards too? I dont know the breed of the dogs