Alpha, beta, delta & theta waves as I recall the different states of mind(vibration). I don't recall where I read it but children up to a certain age are essentially walking around in a daydream state & hence the imaginary friends, events & things they speak of. I do recall reading a book on auras that said children more often speak of seeing auras than adults & speaking from my own experience this was true for me. I remember wondering why the different colors around people & things. Speaking to my parents about this I was told it was just my imagination.

They who dream by day are cognizant of many things which
escape those who dream only by night.
Edgar Allan Poe