pekinese problem

Question
We have recently adopted two pekinese pups, approx 7 mos old.  They are brother and sister and have been in foster care since birth.  We have 3 children, 12, 10, and 5.  THe female has adapted quickly and what seems to be effortlessly.  She loves the kids, is friendly and playful and sociable. The male, on the other hand, almost seems depressed.  He spends most of his day in the kennel, willingly.  In the last few days, he has begun to snap at my daughter.  Each time this has happened, it has been unprovoked.  Whenever she is around, the dog goes straight to his kennel.  He usually will not come out except for first thing in the morning and late at night, when the kids are not out and about.  I have even tried having my daughter help take him outside, go for walks with us, and try giving him treats.  He growls at her whenever she gets near him, and he will not take a treat from her.  
They have only been with us a week and a half, and I know it will take time for him to adapt. He seems to favor me and my oldest son and is very affectionate with us.
I am willing to be patient and help him to feel comfortable with us.  I would, however, like to resolve the issue with him and my daughter.  I want him to be comfortable with her, and vice versa.
His foster mom said when she had them, they were opposite.  He was more outgoing and social, she was more reserved.   I am wondering what has changed this.   She almost seems to be more dominant.
Thanks for your help.


Answer
These dogs are heavily bonded to one another and it is not uncommon for behaviors (such as sociability, fear, etc.) to switch back and forth between them in differing circumstances.  The male is fearful of your daughter.  Young children are a totally different experience from older children and adults; they smell differently, behave erratically (to the dog) and are unpredictable.  This dog is having a very difficult time adjusting to his new environment and especially to the children.  Whenever active aggression is involved, it is absolutely MANDATORY for you to bring in a certified applied animal behaviorist.  It is not ethical to attempt to counsel this behavior in this venue.  A growl is a bite waiting to happen; your daughter is in the line of fire and this puppy is not to blame (nor is the child!)  It would not be unkind (in fact, it might be the best thing) for these two dogs to be separated and a more appropriate (child free) home be found for the male.  You might discuss this with the agency from whom you adopted the dogs.  If you care to treat the problem, you need to find an expert.  The agency itself may have the name of a professional (NOT a dog trainer, you need a dog behavior expert) or you might locate one by calling the veterinary college in your geographical area.  Whatever you DO, do NOT attempt to force or coerce this dog to interact with anyone toward whom he has shown aggression.