Use materials that can be successfully manipulated and sculpted by children, including modeling clay, salt dough, bendable wax or cardboard. Avoid using materials that are dangerous or difficult to form, like sharp wires, metal sheeting or glass.
Secure the materials for the model together using adhesives that are safe for children. These adhesives include craft glue, tacky glue, double-sided tape and paste. Avoid toxic or dangerous adhesives that release fumes or could burn skin, including epoxy, superglue or hot glue.
Paint the model using non-toxic paints like tempera or certain acrylics. Avoid difficult-to-use oil paints or toxic spray paints that release toxic fumes. Apply a base color to the model first, then apply smaller detailing to give the model more depth and dimension.
Create more than one model so that you can test one before the science fair. This enables you to test whether the model will function on the day of the fair, and allows you to have a back-up model in case something happens to the first one.
Attach labels onto the model to demonstrate knowledge about the subject. You can use small pieces of paper attached to toothpicks on which you can write names, or you can write directly onto parts of the model using a paint pen.