Unbreakable Unique Bond
There seems to be a set of rules for taking care of twins. You don’t just have one child to care for; you have two, and they are the same age. They may also have a special bond that makes them prefer each other over a babysitter who is there to ruin their fun.
When one twin ran by with a knife, the babysitter was reading to the other. The person with the knife then tried to hurt another child. All of this is too much!