Last May, my family and I adopted a three legged dog named, Captain, He is a six year old shiz tzu/poodle and the friendliest dog you will ever meet. in the beginning all he wanted was petting and love. He got really attached to the middle child, all he wants to do is be with her and she loves him. However, now he has become aggressive to the youngest, when she walks by him, he growls at her and today he attempted to bite her. We do not know what to do? We love the dog but we love the youngest more. She has been trying to pet him and give him a lot of attention, but she only receives growling. The dog was fine and nice to her before, but then it all changed. This is heartbreaking for the middle and saddening to everyone. This is our first dog, and a very difficult problem. Any advice?