PBS is an excellent website for Language Art. This is used in the primary grades for reading activities
http://www.pbskids.org

NASA is an excellent website for science projects, science activities and science news.
http://www.nasa.gov/audience/forkids/home/index.html

Starfall is an excellent website especially for Kindergarten and First Graders. There are some areas that can be beneficial for Second and Third Graders. This is reading website full of fun activities
http://www.starfall.com

If your child likes to color, this website is full of all kinds of coloring pictures.
http://www.coloring-page.com/online-games/

Increase your typing skills by practicing on Dance Mat Typing.
http://www.dancemattypingguide.com/