Mysterious tracks

Ian and I went on our once-a-year date to do our income tax (yay!) and left the kiddies with Grandma and Grandpa.  When we came back after a few hours they were nowhere to be found!  Not in the house, not outside!  We did spot some mysterious tracks though so after waiting awhile we heard a loud humming noise which gradually got louder.  Then, we saw the "train" come through the trees...

Looks like everyone had a great time!!  

They loved loved loved it!!