How can I teach the difference between strangers and people we know, and safe distances with others?

"Distance from others" is easier to learn when you make the circles of relationships visible (family / close people / people we know / strangers). Draw concentric circles with the child at the center and relationships thinning toward the outside, and decide concretely what interaction is okay for each circle—"hugs are for family," "with strangers, just wave." Rather than an abstract "be careful," it helps to practice checking in the moment, "which circle is this person?" Also convey that distance changes with the person and situation, and that when unsure, it's fine to ask an adult.