It was a gorgeous fall day in Dumbo, Brooklyn, and Keira Cannon was holding one of the weekend photo shoots she does with her favorite subject: her son, Princeton.

Princeton wore leather pants, black-and-white checked sneakers and a black sweatshirt with an open-mouthed vampire graphic. But that wasn’t quite enough flair for his mother. So Ms. Cannon whipped out a purple faux-fur jacket — except that Princeton was, in teenager-speak, “done.”

But Princeton is not a teenager. He is 5 years old. A happy-seeming little boy, he played with his scooter, balanced on the curb, twirled in endless circles but only had so much tolerance for the professional photographer whom Ms. Cannon, 38 and a pastry chef, had hired to populate his Instagram feed, Prince and the Baker, which has more than 5,600 followers.