What is it like to be a baby? Very young children can’t tell us what their experiences are like, and none of us can remember the beginnings of our lives. So it would seem that we have no way of understanding baby consciousness, or even of knowing if babies are conscious at all.

But some fascinating new neuroscience research is changing that. It turns out that when adults dream or have psychedelic experiences, their brains are functioning more like children’s brains. It appears that the experience of babies and young children...