2006 sienna auto start

:headshakeGuys this is the strangest thin ever happened to us. I have 2006 sienna and today my morning around 7.30 when my wife came out along with my 2 sons( 8 and 5) van was already running. We dont have any remote start in our van and it was locked and my wife was holding the key in her hand. We have only 1 key for the ignition. First she thought i have left the van started to warm it up but again she had the key in her hand. she put the key in the ignition and turn it on and turned it off and started again and it did started. She couldnt have left it running a day before bCoz there is no key in the ignition. Is my van have some kind of relay problem. I dont know what to ask. if anybody has encountered same kind of problem pls let me know what it is.

Before you get too concerned. See if it reoccurs. Then come back and post the results.