Reading instruction is a component of the language arts curriculum that should be introduced across multiple subject matter content. Children ultimately have to understand what they read in a variety of textbooks, not just as part of a language arts class. Yet, reading instruction begins long before formal education begins, especially for homeschooling parents and educators.
Worksheets that include topics such as social and natural science will help to expand your child's horizons, teaching them about their environment and how things work, while improving their vocabulary at the same time. A worksheet about farm animals can initiate a visit to the farm area at the zoo, or to a real farm, where your child can explore and learn even more.
Do choose worksheets that are appropriate for the child's level, since children can get discouraged easily, if they are unable to perform the activity. Well illustrated worksheets with cartoons are also more likely to appeal to children. Worksheets that use common situations children come across at home, school, in the market place etc and that use common objects known to children would be more relevant.
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.