Take your kids outdoors for an adventure. Explore your surroundings and collect intriguing items found in nature to use when creating artwork. Your children may have made objects from pinecones at school, but nature offers lots of other fun stuff as well.
Leaves make excellent pieces for creating works of art. Dip them in paint and use them as stamps, or cover them with a coat of clear spray paint or glue mixed with water to preserve them and give them a nice sheen. Glue lots of different shapes and colors of leaves to a background for beautiful botanic artwork. Another way to use leaves is to smooth them flat and secure them to paper with just a little bit of glue stick then paint over them. When the paint starts to get tacky, gently pull the leaves off for a reverse leaf pattern.
Twigs and sticks make cool stuff too. Glue them together to make frames for you natural art pieces. Paint them and make a sculpture from them, or add them to your leaf design. Tree bark is another good choice and can be used in the same ways.
You can also pick wild flowers (and weeds that look like flowers to children, such as dandelions), and dry or press them. Press between two pieces of glass and frame to make a pretty three-dimensional picture.
Acorns are fun to work with and they can be used to make all sorts of cool things. A car made from sticks would not be complete without acorn tires.
Rocks are also great. Clean many different sizes, shapes, colors, and textures. Your kids can clean and polish them, or they can paint them to look like animals, flowers, faces, or anything they like.
Speaking of painting, weeds and thick grasses make great paintbrushes. Kids can spread or splatter paint with them to make unique and interesting designs (this is of course best done outside).