The most distinct feature of a U-shaped kids' toothbrush is its U-shaped head, which is designed to fit around the child's teeth and gums. This shape allows for simultaneous brushing of both the top and bottom teeth, making it easier and more efficient for children to brush their teeth. Kids' toothbrushes typically have soft bristles to ensure gentle brushing and prevent damage to the child's delicate gums and tooth enamel. Soft bristles are also more comfortable for children, encouraging them to maintain good oral hygiene habits.