Potty training incentive!

For months now, we have had this Thomas the tank engine Steam track set. Finn has known that when he went poo poo and pee pee in the potty, he got to play with it. I bought it thinking that he would jump at the chance to play with it and instantly be potty trained. What am I, a rookie? You betcha! Needless to say, he drug the box around the house showing everyone that THIS was what he got when he went in the toilet but he didn't actually do it. That is, until 2 weeks ago. Since then, he has only had two days where he has had accidents, that is pretty impressive I think but then, I am the mom.