Teaching reading and other language arts skills to preschool learners relies heavily on a concept known as modeling. Modeling merely means exposing young children to the types of behaviors and habits we want them to learn. Many parents and homeschooling educators employ this kind of instruction naturally, without giving it much thought.
Since 3rd grade math relies on the concepts that were learned during kindergarten, first and second grades, don't be afraid to start your child at a lower level.
A comprehensive set of worksheets covering a variety of subjects can be used to expand your child's learning experience. A worksheet about shapes can be used as part of a game to find shapes around the house, counting worksheets can be used to count things you see in the grocery store and so on.
A homeschooled student will receive the absolute best education possible without the expense and overhead of ordering multiple copies of hardcopy texts. Textbooks will not need to be discarded at the end each school year.