There are a few things you can count on when you watch Kids Baking Championship: adorable contestants, surprisingly grown-up desserts and, inevitably, some tears. Usually it’s the kids who cry, but during the third season (which premieres January 2), Duff gets emotional, too. “They were just baking their hearts out. I couldn’t help it,” he says. It’s easy to understand why he and cohost Valerie Bertinelli become so attached to their pint-size protégés: The two stars not only host the show, they also serve as mentors and judges, spending up to six hours a day critiquing, consoling and, yes, even crying with the contestants. Valerie and Duff have a great on-screen dynamic, and the same holds true off set: They’re constantly poking fun at each other, and they frequently finish…