I really don't think we can help you with this decision since we don't know the kid. All kids have tendancies to do certain things when the parents aren't around but all kids are different.
I just bought my first Porsche and I plan on it being the vehicle my kids learn to drive in and I anticipate giving it to the oldest at that time and replacing it with a newer model for myself.
Base your decision upon your kid, you either trust them or you don't. They have given you reason to trust them or they haven't.
Best of luck either way.
