A few mounths ago i had a dream that my grandparents dog went nutts.I was picking up empty soda cans and out of the corner of my eye I saw Barny(are
dog) about to jump on my 1 and a half year old sister. I shouted no Barny five times(normally he is a great dog)but he jumped on her anyways.
It's probably an extension of natural concern.... Big dog, small child...so the fear manifested itself in your dream so you could deal with it...
Unless of course, your dog is a chihuahua...and then we're back to square 1, hehe....