A childhood belief about money

From 1909 to 1958 American pennies had Abraham Lincoln on the front and wheat on the back. (They now have the Lincoln Memorial on the back.) When I was growing up in the '80s, my mom would sometimes find "wheat pennies" in change she recieved. She kept them in a jar and told me they were special since they were old. I thought they were called "weak pennies" because they were old. I also though the wheat magically appeared on the back of a penny when it got old enough.