Toys from Trash
Toys from Trash-awesome website, who needs tv
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.
Turn the night sky into slime.
35 Magical Science Experiments for Kids
There is so much to learn about leaves -- structure, shape, color, … These are fun science activities for kids to learn about leaves. They are so fun and easy, that a preschooler can enjoy them.
Cute DIY Paper Plane Toy (with free template) - contributed by La Maison de Loulou
Peekaboo Toy Jointed Doll templates by Mr Printables
Straw Weaving -- 29 creative activities for kids that adults will actually enjoy doing, too!