They are actually check marks, not boxes, FYI. I added them as text from the character map tool that's part of the Mac OS. And I figured out how to do this.For the benefit of anyone else trying to do this, here's what I did:

I created my list with the checkmarks:

✓1. Start the car
✓2. Drive the car
✓3. Stop the car

I selected the checkmarks and made them transparent. I set the text to appear at once (all together) on a mouse click.

I then duplicated the text block. On this copy, I made the checkmarks solid and all the words transparent. I then set the animation to appear one line at a time. Then I placed this text bock directly over the first one.

Result: 1st mouse click, the entire list appears without checkmarks. 2nd click, a checkmark appears next to the 1st item, 3rd click a checkmark appears next to the 2nd item, etc.

This may not be the most elegant way to do this, but it was easy and it works.