My mom had a phone call similar to this about 5 years ago. The caller said “Hi Grandma, this is Nathan.” Mom was immediately on the alert because 1.) No one calls her grandma, but rather something shorter, and 2.) Nathan had never called my mom before and was only about 14 when this call took place. But, the caller sounded young, so she didn’t hang up right away, in case it was him. He then said he had been in an accident and needed money, etc… She hung up.
I agree with @MWolf . If someone young called in a panic, crying, saying “Mom, mom, help me!”, the first instinct is probably not “This is a scam.” I have a daughter and a son. I think it would be hard for me to fall for a male pretending to be my son, as his voice is very distinctive, but I’m not so sure about my daughter.
Luckily, I have read a lot of these stories in the last year or so, and I think I would be suspicious. But I love the idea of a safe word anyway. I’ve thought of that before, so no time like the present.
I’m linking the Scams thread, so people can be aware. http://talk.collegeconfidential.com/t/scams-youve-encountered
Edit: The phone call was actually creepy because my mom has an unlisted phone number and my nephew was only 14, so how did they get her number and his name? That was the scary bit.