Not to go near occupied cars. It only takes a moment for a car door to open and a child to disappear. Children are trusting. A stranger is anyone you and your child do not know and trust. This includes casual acquaintances and even people dressed in a uniform, such as nurses and security guards.
Strangers can be kind and friendly, but they are still strangers.
To go places in a group, not alone. It can be a helping-hand home, a store, the police station, a firehouse. Hiding leaves him vulnerable. That adults rarely ask children for directions or help. A secret family password.