You would have to setup your car as a controllable device, and then setup the permissions in your home. I seriously doubt this will ever be possible or allowed.Unsure, but when the app comes you'll be able to do it via that.
I know Google works from your car to your home (turn on lights and open garage doors etc...) but unclear if it works from home to car.
Personally I'm not sure I want my son asking Google stuff that could affect my car! 😂