I've forgotten the name of the paper but I read a fairly in-depth report on human/dog co-evolution and how it has ingrained an instinctual understanding into each other even as little more than babies for both species.

We also tend to share our babies with dogs. My sister has recently had skin dogs and my fur babies are very interested in standing by the bassinet and watching over them. They're also extremely patient with their flailing hands and curious fingers.

While the reasons why aren't all peachy, and much of the framework it happens in is incredibly abusive and horrible, what humans and dogs share is very beautiful.

My dog recently broke her leg, she was screaming in terrible pain, but she went dead silent when we arrived and started investigating. That level of trust is incredible. I don't know exactly what's going on in her head, but I know that when something is wrong and I show up to help her breathing calms and she relaxes. Just as when I think I hear something in the night or whatever I look to her for guidance on whether it's a threat.

Meh, dogs have been selectively bred for millennia to bring things to people. They're also completely dependent on humans not only for nutrition, but also probably in this case behavioural guidance.

It's not so much "here human I trust you so much I'll let you hold my baby" as it is "here human this smells important".