http://www.exploratorium.edu
This site is a fantastic reference. It has ideas that have been submitted by classroom teachers. Children could access and peruse this site with adult assistance.
http://www.go2dsc.org/funstuff.htm
This site has a number of wonderful science activities on it. Not too much directly related to electronics and magnetism, but could be a super resource. Children could access and peruse this site with adult assistance.
http://www.oakview.fcps.edu/~glazewsk/96-97/scientist/index.html
This site was designed by a group of elementary school students at the Oakview School in Virginia. It has some great ideas! It is also a site that children could access and peruse with adult assistance.
http://teacher.nsrl.rochester.edu/phy_labs/AppendixE/AppendixE.html
This site has some more advanced information on use and application of the scientific method