Try to have your subjects facing toward the sunlight so that their faces are not in shadow. The overwhelming brightness of the snow will cause your camera's meter to underexpose the detail of shadow areas.
An alternative solution to help alleviate dark shadows is to use your cameras "fill-flash" mode. Also, check the background surrounding your subjects. Make sure there are no distant objects aligned with your subject (such as bare trees and limbs) that would add an unwanted character to your picture (as here, there is a tree growing out of one of the subject's head!)

Position the sun at your back when taking outdoor pictures, so that the subject is brightly lit. Try not to have your subject facing directly into the sun, causing them to squint, but rather at an angle so they are comfortably looking at you.