My 12 year old niece is still grieving over the loss of her childhood dog.
A few months before she was born, my sister bought a Labrador Retriever puppy for Casey(my niece)'s half brother. After Casey was born, Sherman (the dog) became more like Casey's dog. She did everything with him. They'd cuddle, he'd sleep in her room, she talked to him, etc. Even after Casey got a puppy of her own, she still always favored Sherman. She referred to him as her best friend.