Gather 100 pennies, ten dimes, some dollar bills and paper and pencil. Children at this stage should be familiar with the value of the coins and how they are related. Use prior knowledge to demonstrate that ten pennies are equal to one dime and 10 dimes are equal to one dollar. Allow them to discover other equalities with the money.
After the child's discovery, review what a fraction is. Using pennies, place one penny over 10 pennies and say "one-tenth." Explain that one penny is one-tenth of the ten pennies. Continue to model and then have the child model understanding by using a variety of pennies as the numerator. Then substitute the 10 pennies in the denominator with a dime and discuss value of the coins. Again, make a variety of fractions based on the value of the coins instead of the number of coins. Extend this into using dimes and a dollar bill. Show that one penny over a dime is one-tenth, but so is one dime over a dollar. Be sure they understand that a dime is one-tenth of a dollar, and two dimes are two-tenths of a dollar. Begin using the paper and pencil to write these fractions.
Review the value fractions of one penny to one dime. Again say "one-tenth" and write the fraction "1/10." Ask if the child knows another way to write one-tenth. If not, write "1/10=0.1." Explain that a decimal is also a part of a whole number, just like a fraction. At this point, it would be helpful to review place value. A place value chart may also be helpful. Continue to make fractions with the pennies and dimes and then convert to decimals, making sure to say the numbers correctly: "three tenths," and not "zero point three," for example. Eventually use pennies and the dollar. For example, place seven pennies over the dollar and say "seven-hundredths," and write "7/100" and "0.07." Continue to practice with a variety of coins and check for confusion. Again, use place value chart as needed.
Once the child has grasped the concept and can clearly show an understanding of basic tenths and hundredths, add nickels and quarters to the pile to show one-half, one-fourth and one-fifth. By putting a nickel with a dime, the child can say it is one-half of the dime's value. Using pennies to substitute as needed, you can demonstrate how one-half is equal to five-tenths and 0.5. Continue with other coins allowing the child to explore the coin values by making a variety of fractions and converting them to decimals.