I had a similar problem years ago. The shelter said the yellow lab was a wonderful dog, loved everyone, etc. When we had her home a few days I notice she would stare at my son then about 3 years old in a menacing way. Then one day as my older Greyhound was just walking past her she struck out and tore the top of my Grey's head badly. She went back to the shelter that day with a warning that she should not be placed in a home with other dogs or kids.