Harry tells them
Harry sat in the car looking at the umbrella and thinking that he needed a stick instead when it suddenly was a stick, a walking stick to be exact. Blinking he then said, "how the umbrella turn into a walking stick?"
Blinking Mycroft said, "magic is my guess little one."
"Oh, what's magic?" asked Harry.
Surprisingly it was John who answered with, "no one knows exactly what it is, some say technology long forgotten and others say an inborn ability." looking around John sees the shock on both faces and says, "what my mom and dad used homeschooling and Hogwarts to keep me up to date for my education."
Smiling Harry asked, "really? Can I do that?"
At that John nods and says, "great idea harry, we can do that for both you and Hermione."
He nodded and asked, "can I eat something? I'm hungry."