They see more than your physical body on average. The downside is that they can't express it with words adults would understand, therefore the secret persists.
Discussion
Why do they lose that ability?
I will speculate now because I suspect anyone knowing the answer for a fact is never coming back here. So here it goes. It's a mixture of indoctrination aka schooling, bad nutrition, distractions, retarded parenting as a consequence of their schooling, peer pressure and so on.
0-7y is a very special time in a child's life for many reasons. It's like a trial period and a blueprint for the rest of their life. Tbf, a fringe minority get to keep such abilities later on. Again, I'm speculating. Hope it helps in your quest.
some of us never quite lose that, it's like seeing with your heart