I kind of agree, but I have more tolerance for it here mostly because, despite the fact that the killing is a horrific act, David isn't really standing in the role of a kid for purposes of the story - he's not the helpless, powerless one. From the POV of the animals, and his victims in particular, he's already hit the Dahmer mark.
The other reason death of kids -- be it David or Ty and Chloe -- doesn't annoy me here as it does when it happens in the Big Two is that this is the first time that things have gotten so grim in this particular fiction. The protagonists are learning that, as much as they think they've had experience with the supernatural, they can still get in way over their heads. For them, this is a scarring experience, whereas if a kid gets horribly mutilated over in X-Force, it's just Tuesday.