My dogs anxiety

Question
We have a terrier mix (sort of looks like Benji in the face) that we rescued from a local animal shelter.  We have had him (Tucker) since April and were told he was abused as a pup.  He is one year old.  He has been very timid and shy since we got him but is a lot better.  However, lately he has been yelping for no apparent reason and then shivering and slinking away with tail down.  We show him all kinds of love and attention and this has us really preplexed.  Recently, my husbands daughter and her two little boys moved in with us for a while.  We already know Tucker does not feel comfortable around children because of the way he acts around our other grandchildren.  Can this be the cause?  Please help if you can.  

Answer
If noone is around your dog at the time this yelping is going on, then I would probably guess some type of phsical problem.  Check him out for neck or back injuries or hips.  If someone is around then watch carefully the sequence of events and you will have to work with a trainer.
 If this is not physical, then you may want to do some agility training with him.  I have an older group of agility people who train their dogs with me.  The dogs become more confident in themselves and everyone has fun.
nancy