Sounds a bit like false memory. As soon as i read the description i feel like yeah i know this guy, just because i imagine him. People on the internet love these me-too stories. What kids have in common for sure is the desire to move as described. It's our attention that moves in such ways, as we grow a comprehension of our environment. This is actually an excellent example of what the sensing function does. But projecting this desire into a dissociated day-dream character - "my little Si demon" - is very special and unnecessary. As a former skateboarder i also have the imaginary "fingerboard" character, who skates every object on my desk. I mean, my hands and my attention do this and its not necessary to think of it as a character. This is an example of what the ego does. It personalizes every fucking thing under the sun. If a pine cone falls on your head, god himself must have willed it to do so. If my hand skates the edges of my mousepad, that must have been the doing of greyson fletcher
, the viking goddess of skateboarding. Ego is false memory. After the fact fabulation. I wrote this, it must be true because I am not a false god. I totally exist, bitch.