NEW YORK — Nickelodeon Prods. has promoted three of its senior executives, citing the moves as a follow-up to its plan to double the network’s output of original animation and to kick off daily original preschool programming on Nick Jr.The three executives are Marjorie Cohn, Kevin Kay and Brown Johnson. Cohn, VP, current programming, Nickelodeon, becomes VP, executive producer, current series. Kay, executive producer for Nickelodeon’s producers’ group, shifts to VP, executive producer, development. Johnson goes from VP to senior VP of Nick Jr.