I've attempted to parent the glasses specifically to the head bone by going into object mode, selecting first the glasses, then the armature, and then switching into pose mode and only selecting the head bone. I got a box that came up and the only option was "connected". Thought I was on the right track, but the glasses still wouldn't move when I posed the character.
I am on mac and could possibly be hitting the wrong buttons on my keyboard? I'm not really sure. I used to be able to attach a hat to a character earlier this year, but nothing I remember seems to work and I can't find anything online that works either.