Talking to your mother has the same effect as a hug and can help reduce stress levels. The hormone oxytocin is released when the kids heard their mothers' voices.
An interesting study by researchers at the University of Wisconsin in Madison explored the power of voice in times of stress. Sixty-one children were exposed to a stressful situation in the study: public speaking, followed by solving mathematical problems in front of an audience. When you're stressed, your body produces a hormone called cortisol. As these children underwent this stressful situation, their cortisol levels went up dramatically.
The researchers then looked at the effect of the same stressful event when the children interacted with their mothers right afterward. They either talked with their mothers by phone or were reunited with them physically for comfort. Following either physical contact or just hearing their mothers' voices, the kids' stress hormone levels decreased, and they also reported feeling less stressed. What's more, there was no difference between those who heard their mothers' voices versus those who had personal contact.
The authors found that in both groups of children, the hormone oxytocin was released when the kids heard their mothers' voices or were in contact with their moms.