Bad Machinery 2: The Case of the Good Boy: 09/16/15
The Case of the Good Boy by John Allison is the second printed collection of the Bad Machinery webcomic. It's also online on the Scary Go Round site.
I'm putting all those links first because I'm hoping you'll take the time and read the webcomic.
Anyway, these cases are a West Yorkshire version of the X Files or Supernatural, with mysteries being solved by students while still attending school and doing all the other stuff teenagers do.
In this one, toddlers and babies are going missing, taken by large dogs or wolves. Their disappearances correspond with a visiting carnival. There is a connection but not in the Something Wicked This Way Comes manner.
Although the teens don't necessarily like having to babysit their younger siblings, they do genuinely like kids. They are as worried about their disappearances as the adults. They also have some paranormal experiences to draw on, making them more alert to possible solutions.