Trying to motivate your child to pick up...this is a little silly because by the time you have placed all the pennies you, personally, could have cleaned up the entire play area...however, your child would not have helped. So on a rainy day when he/she has pulled out every toy and it is time to clean up..make it fun!
Hide some pennies or stickers underneath some of the toys. Then tell them that they need to find the pennies. The trick is that if they pick up a toy to find a penny they have to put it away..whether there is a penny there or not.
I found that when I did this, my son was a little over three and he had a hard time remembering to put the things away. I had to watch and remind. But he had a fun time and got super excited.