"ABCya.com is the leader in free educational kids computer games and activities for elementary students to learn on the web. All children's educational computer activities were created or approved by certified school teachers. All educational games are free and are modeled from primary grade lessons and enhanced to provide an interactive way for children to learn."
Magnetic Slime--really neat, but it requires liquid starch, iron oxide powder, and really strong neodymium magnets. There is a commercially available magnet putty that might be a good substitute for exploration.