[Heel n Toe]

Found the entire Bixby short story online...
It's A Good Life: Jerome Bixby

I was a little off in my memory of some of the details in that part about the grocery store delivery guy and Anthony... but I was close enough.

As Bill Soames pumped the pedals, he was wishing deep down that he could pump twice as fast, to get away from Anthony all the faster, and away from Aunt Amy, who sometimes just forgot how careful you had to be. And he shouldn't have thought that. Because Anthony caught it. He caught the desire to get away from the Fremont house as if it was something bad, and his purple gaze blinked and he snapped a small, sulky thought after Bill Soames--just a small one, because he was in a good mood today, and besides, he liked Bill Soames, or at least didn't dislike him, at least today. Bill Soames wanted to go away--so, petulantly, Anthony helped him.

Pedaling with superhuman speed--or rather, appearing to, because in reality the bicycle was pedaling him--Bill Soames vanished down the road in a cloud of dust, his thin, terrified wail drifting back across the heat.