John's Children Puns

My dad's a doctor / teacher and his workplace was close to my university, so he often took me to class in this busted '83 BMW-320 which he bought brand new. This one time he arranged for one of his former students (John, now teacher as well) to take us, and he shows up in a brand new Audi A4. We get out of the car and i ask him:

-"Dad, how come John has a brand new Audi A4 and you're still driving the same busted car you've had since I was born?"

-"John doesn't have any children."