Tone of voice is very important in human conversation. A person might use words that communicate one message and a tone that shows something very different. This possibility for confusion is one reason that businessmen encourage discussing things in person, rather than through email, as tone cannot be determined in the written form.
The same rule is true with children. Children as young as a few months respond to a change in voice. It has been recorded that babies prefer to hear a story read by their own mother rather than another woman whom they do not know.