One of the fourth graders has diabetes, the school librarian tells David Ceron, who is getting ready backstage. It’s not the first time a young student attending one of Ceron’s presentations has had the disease. When that happens, Ceron watches his words more carefully. It can be difficult to talk to kids with enough gravity that they take the dangers of diabetes seriously without scaring them.On this late-September day, the student has type 1 diabetes, so Ceron decides to discuss the different kinds of the disease. There’s nothing you can do to avoid type 1 if you’re born predisposed to it, he tells the children who’ve gathered in the gymnasium at Canterbury Elementary School in Edinburg, just north of Ceron’s hometown of McAllen. “Nick Jonas…