She was hooked.
She ran some more 1/2 mile kids' runs and a one miler. Then at age 4 she announced she wanted to run the 5K on Thanksgiving which would be just after her fifth birthday. Her mother and I ran with her. (Slowest 5k I've ever run) Full story here. She ran the first 2 miles and the last .1.
While in the jogging stroller with me and my wife on a 6 mile run she told us she wanted to run, she does that sometimes and usually goes 1/2 mile to a mile. This time we let her out at the turn around point and she ran the whole three miles home.
She let us know that at the Butterflies for Maddie race this year she is not running the 1/2 mile, she wants to run the 5K. Actually she wanted to run both, but we told her she had to choose.
She loves to run and at age 5 is capable of running a 5K. She even rode her bike (training wheels and all) five miles to get ice cream.
The reason she loves to run and bike and exercise is simple. Her family has set the example. Her mother, her big sister, and I all take good care of our bodies, exercise, make healthy food choices. It is what she has grown up knowing and it is what she does.
To really teach something, to really instill something in your children, my advice is to live it for yourself.