The Bible says they are "ministering spirits sent forth to minister for those who will inherit salvation" (Heb 1:14). Jesus said, speaking of little children, "in heaven their angels always see the face of my Father who is in heaven" (Matt 18:10).
Because of these verses, some people believe in guardian angels; that is to say, angels who are specifically assigned to care for individuals.
Leonard LeSourd tells of Jack and Jenny Pate, who were decorating an upstairs room in their home. It was a warm day, and the window was open. As they were busy paperhanging, their three-year-old daughter Peggy amused herself by taking leftover scraps of wallpaper, dropping them through the window and watching them float on the breeze to the ground below.
Eventually, she leaned out a little too far. Her father looked up just in time to see her disappearing through the window. Underneath the window was a concrete patio with three steps with sharp edges. If she hit one of those, it could be fatal.
Jack let out a single word of prayer. "Jesus!" He and his wife practically flew down the stairs and through the front door. Peggy was sitting on one of the steps, completely unhurt. "Don't worry," she said. "That big man caught me."
The house was in open country. They would be able to see anyone walking away.
They looked all round the house. There was no one there.
 Leonard LeSourd, ed. Love on its Knees. London: Hodder and Stoughton, 1998, p218.