change in temperment

Question
We have a 3 year old spayed boxer mix that has been part of our family since birth.  She has always been protective of the family unit but only by barking. In the last month has become very aggressive to anyone not in the unit and she bit the child of a friend and tried to bite another child.  We are no longer allowing her around children.  The only change in our household as been the addition of 2 high school exchange students.  Could this be the cause of the aggression?

Answer
Yes. Any severe change such as adding non-family members will cause territorial and protective aggression.

However, it is not normal for any Boxer to harm a child- whatever breed she is mixed with-- is the cause for her biting children-- not the Boxer in her. Boxers never harm children.