If anyone can help I'd really appreciate it. Yesterday while my four year old was sitting in my front seat of my Toyota Sienna without a key in the ignition the van was able to slip into gear, roll down my driveway, across the street and into the woods. It's most likely totaled. No one got hurt, thank God but how does this happen? Anyone have any idea?
Thank you,
Renee

What year is the vehicle? There are safety devices to keep this kind of thing from happening, some require the use of the brake pedal, and the key has to in the ignition to the unlock position before the shifter can be moved, and others the use of a key. You need to check and see if you can take it out off gear without the key.....and if you can, the ignition switch and parts of are defective.

It is a 2004. Everything seemed to be OK, but obviously it wasn't. Any recommendations on who to have look at this issue?

The first thing is to check if the vehicle has any recalls on it, then consult with a known reliable mechanic,....the dealerships are costly but its your choice.