Show children a simple calculator with all of the basic functions, including addition, subtraction, multiplication and division. Point out what each of the keys does and how important it is to touch the keys in the correct order to get the answer. For example, show them what happens if you choose to push 8 divided by 48 instead of 48 divided by 8. Show children how to use the decimal point if they are solving an equation with money.
Allow children to explore the calculator on their own. Encourage them to solve large addition problems, add and subtract money and multiply and divide large numbers. When they seem to understand the basic functions of the calculator, verbally give them a simple equation to solve, such as 23 plus 13. Make sure they are pushing the buttons in the correct order and clearing the calculator after solving the problem.
Have a calculator race with children. Before the game, create several index cards with simple math equations written on them for children to solve. Deal these equations to each child participating in the race, face down. At the sound of a bell or a whistle, have each child turn over the cards and begin solving the problems using their calculators. Have the child write the answer on the index card in pencil as they solve the equation. The first child who completes his index cards correctly earns a small prize. To extend this activity, increase the difficulty of the math equations you present. Add problems that require more than one mathematical operation, or use word problems.