Our dog acted vicious at the kennel

Question
We have a neutered three year old black lab/ blue heeler mix that we adopted
as a puppy three years ago.  He has always been friendly and patient with
children, adults and other dogs. We boarded him for the second time at a
new kennel over Thanksgiving.  The day we were scheduled to pick him up we
received a call from them saying that he had turned vicious, they were not
able to bathe him, or even get near him.  He nearly chewed through the chain
link fence trying to attack the dog next to him and they had to isolate him.  
We picked him up and he has acted relatively normal, a little lethargic, but
basically the same as always.  We're concerned because we have small
children at home and cannot risk him turning on them.  He has always been
docile and fun loving, this incident came out of the blue.  Should we be
concerned for our children?  What could have caused this change?

Answer
I have worked in a kennel and have seen this a few times-and this sounds like it may in fact have been the dog next to yours that caused your dog to become very upset,sometimes if a dog is next to an agressive dog it will upset the other dog to the point of it trying to fight back

And often a dog aggressive dog won't be the one that seems like the aggresser as it's often staring and 'silent cues' that cause other dogs to want to fight with that dog

so from my experience it was most likely the dog next to yours that was the problem,not your dog