Introduce the term natural numbers to the class, which describe the normal numbers people use to count, in number-order. Examples of natural numbers include 1, 2, 3, 4, 5 and so forth. Reinforce natural numbers by counting a number of objects in the class or by doing a connect-the-dots type of art project.
Introduce the terms whole numbers, which include the natural numbers and the number zero as well, along with fractions and mixed numbers to the class. Differentiate between whole numbers, fractions and mixed numbers by showing the class a set of measuring cups and rice. Scoop some rice into a one cup-sized measuring cup and show that it is full of the rice. It is one whole cup of rice. Empty half of the rice into a container to show that it is only half, a fraction of the way, full. Scoop another one cup-sized measuring cup to show that you now have 1 1/2 cups of rice, a mixed number because it includes a whole number and a fraction.
Introduce integers, which include positive natural numbers, the number zero and negative numbers. Use a number line to show students numbers on the right side of zero are positive and that numbers to the left of zero are negative. Reinforce the concept of a number line by allowing students to create their own number line, and move a marker, such as a penny, back and forth along the line. Check for comprehension by having students place their penny on the 0 and the move it two spaces to the negative side, and then four spaces in the positive direction. Students who understand how a number line works will have their marker on the number two at the end of the short exercise.