Starting Early: Pros
While these opinions are valid, in a traditional school setting, Kindergarteners are learning basic skills. They are learning sight words, phonics, and counting, upper case and lowercase letters,and simple math and money skills. They also are given an introduction to science through learning about animals, seasons, and the five senses, among other things. For social studies, or history, Kindergarteners are taught about mapping skills, cultural awareness, and information about the community. World Book puts out a typical course of study for each grade level. They highlight 67 things Kindergarteners could learn by the end of the year.
If your child was to skip Kindergarten and just begin with First Grade material, some of these skills would be missed, possibly creating more work to backtrack once you've begun. The beauty of homeschooling is that you can create a schedule that is as light or as heavy as you'd like it to be for your Kindergartener. By beginning with Kindergarten material you are staying in pace with traditional schools. While this may not be important to every family, if it is important to you, this would also be a good reason to start at this grade level.
If you begin homeschooling in Kindergarten you are also laying a foundation for future years, in regards to structure. For example, even if you do an hour of work a day, you are starting to show your child that there will be a time set aside each day for education.