First off, the front passenger seat is a much better choice than the backseat in these cars. That back seat is for groceries, kids and people you don't like very much.
Run the seat back all the way, recline it all the way and you'd be surprised how much room there is for two.

How many of those kids have gotten hurt or killed? How many of the cars have been wrecked?

There's a reason insurance for young males is so high. It's based on claims paid.

Putting a young, inexperienced male behind the wheel of a powerful car is foolish. Thinking that "My son is different, He wouldn't do that" is nothing more that fooling yourself.

And I'd bet very heavily that your son drives just a little different when you aren't watching.
We all did.

Some of us still do, but we do it with more experience and better judgement (usually learned the hard way).

I do have to say that it was smart not to let him have a motorcycle. I'm of the opinion that a driver should have at least a couple years behind the wheel (learning how idiotic other drivers can be) and have their first accident before getting on two wheels.