I'm not Diederich but I'll deconstruct your hypothetical in order to contrast it with her/his example.
* 9pm. Late, approaching curfew for children in many municipalities.
* 3-year-old. I have yet to meet a 3-year-old who can handle being free-range.
* Your yard. This is your neighborhood and you don't recognize this child. This is vastly different from being at a public playground where there are many unfamiliar children.
* Trouble communicating. A typical 3-year-old should be able to communicate. If not, she most likely can't handle being alone.
* Shoeless. I'm not sure this is relevant unless weather conditions are austere or your neighborhood contains broken glass.
The cumulative of these elements leads to an out-of-the-ordinary situation. It implies neglect. A search for the parents or if you're too busy, a phone call to police non-emergency is probably the appropriate response.
* 9pm. Late, approaching curfew for children in many municipalities.
* 3-year-old. I have yet to meet a 3-year-old who can handle being free-range.
* Your yard. This is your neighborhood and you don't recognize this child. This is vastly different from being at a public playground where there are many unfamiliar children.
* Trouble communicating. A typical 3-year-old should be able to communicate. If not, she most likely can't handle being alone.
* Shoeless. I'm not sure this is relevant unless weather conditions are austere or your neighborhood contains broken glass.
The cumulative of these elements leads to an out-of-the-ordinary situation. It implies neglect. A search for the parents or if you're too busy, a phone call to police non-emergency is probably the appropriate response.