One of the few (and last) times I ever babysat, someone called the house. The girl was allowed to answer the phone as she was about 11 or 12. It was a very brief conversation and I asked her what they had said. She said they asked if get parents were home and she had said no. When I asked her what he said, she told me all he responded with was "good." And hung up. I freaked out and still get shivers about it to this day. Luckily, the parents came home about a half hour later and I had to explain to them why the curtains were all closed and we had shut ourselves in the basement.
TL;DR don't let the kid you're babysitting answer the phone. Ever.