I haven't been on Disney either but have been on Carnival, RCCL, Celebrity, Princess and Holland America. I have never seen a deck railing of glass with the exception of the balconies and around the pool areas.
As far as the exact width between the railings, I have never been inclined to measure same but it would have to be a very small child that could fit through one. I would be far more afraid of a small child climbing up and falling over the rail than through it. Parents need to watch their kids whether on a ship or a shopping mall.
Family cruiser, If I may be so bold as to ask, just why is it that you always seem to be on the lookout to say something contrary to cruising, make negative statements about cruising and the cruise lines, the ships, etc. etc. Also, it seems that you just wait for someone on the staff to make a comment that you can pounce on if it's contrary to the way you see something. Honestly, is there any positive thing or things you could mention about cruising ? Just honestly curious.