Warners’ “Where the Wild Things Are” opened to an estimated $32.5 million for three days, at the upper end of expectations. What’s interesting is that this adaptation of Maurice Sendak’s beloved 1963 children’s book is playing to audiences packed Gen Y (including those Williamsburg hipsters) and aging Gen Xers despite its PG rating. Most family movies show a substantial increase from Friday to Saturday during their opening weekend, but the bump for “Wild Things” was only 2 percent, confounding predictions by some that the picture would finish closer to $40 million after a stronger-than-expected $12.5 million opening day. Overture’s revenge thriller “Law Abiding Citizen,” which wasn’t expected by many to make it out of the single digit millions, surprised in second place with a robust $21.5 million for this Gerard Butler-Jamie Foxx vehicle.  “Paranormal Activity” was in third, pulling in a hearty $20.1 million at a just-less-than-wide 750 locations before taking on “Saw VI” in wide release next weekend. Last weekend’s leader, “Couples Retreat,” tumbled  to fourth and  $17.9 million and Sony’s remake of “The Stepfather” with Dylan Walsh ended up with a slightly better-than-expected $12.5 million.