How can I remap the right mouse button to the left mouse button? My googling abilities have failed me and I can't figure out how to remap the mouse buttons.

My 3 year old niece is having trouble using the mouse on the computer because she is right clicking by accident. Since she is so little I thought it would be nice to just remap them until she gets older. Is this possible?

Computer: 13" 2010 Macbook Pro with OSX 10.8
What mouse? Apple's Mighty Mouse is configurable as a one-button mouse. For other mice, look at the USB Overdrive mouse driver. It's an amazingly configurable driver for mice, trackpads, joy sticks, game controllers, and other HIDs. I used it with a Kensington multi-button trackball before I had the OEM driver for it. I'd be surprised if you couldn't configure most any mouse as a one-button mouse.