Physical activity is not only important for your child's health - it will help them cope with the sheer physicality of interacting with twenty children on the playground. Bumps and shoves are inevitable, so make sure your child has lots of physical play to develop gross motor skills too.
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.
Third grade can be particularly challenging when it comes to math, as this is the year that students are learning about fractions, measuring and weighing objects, graphing and counting money. Most importantly, third graders should be comfortable with the basics of math such as adding, subtracting, multiplying and dividing. If your child isn't comfortable with these basic components, it's almost inevitable that he or she will struggle with future math lessons.
By the time your child is ready for kindergarten or school, they should be able to recognize their own name and other simple written words. The sounds of each letter of the alphabet should be familiar to your child, and they should understand the principle of reading from left to right, which way to hold a book, and possibly even be starting to read three and four-letter words.