Whew! You had me worried I had a big head!!!!........................No jokes please!!!I bought a pocket square to wear as a head band and also around my neck. IT DID NOT FIT ME! I wear a medium in hats and the thing just would not fit. I would try it on at the store before purchasing it.
I am afraid to try and have to come back and tell you that my head is too big even with your triangle suggestion.I you fold a pocket square in half to make a triangle shape, then roll it(or fold more) to make it as a head band, it will have plenty of space left to tie on the bottom.
Did you fold it in half that makes a rectangle shape? If you do that, it's not even going to fit on a baby's head!!!