Baby Center cites studies that show that different learning styles in children do exist, and that most children exhibit some measure of visual learning, usually combined with auditory learning. Because of this, showing groups of preschoolers visual aids when addressing basic concepts, from colors and animals to telling time, ensures that all of your students will benefit -- some by your auditory explanation, some by the visual aid and the vast majority by the combination of the two.
Children love looking at pictures; hence the widespread popularity of children's picture books. When introducing a subject that could be challenging for children of preschool age, such as telling time, showing a visual aid can also help the child understand the information simply by keeping her attention focused on the subject at hand. Furthermore, it reinforces the lesson for children who learn primarily visually.
Using visual aids is also another way of reinforcing lessons about senses and sensory information. As students learn what it means to see, hear, smell, taste and touch, brightly colored visual aids can reinforce the sense of sight, showing its importance to the students and reinforcing the lesson in their memories with the use of carefully chosen aids.
Visual learners assimilate information by processing it through images; telling them the word "cat," for example, will most likely conjure a picture of a cat in their minds. Therefore, teaching them concepts with corresponding images means that they will be more able to recall these concepts later on, by relying on their memory of the image that introduced the concept to them.