Kes
I'll Decide ...
That works for you until that child gets a serious injury and then the parents come for you because you said you were fine for them to play. I know I'm being cynical and over cautious and maybe a spoil sport stopping a child from playing football and I have received a lot of stick when I've enforced this but I just don't trust that this won't come back on me if something goes wrong
Your responsibility lies within the LOTG and being the referee. Your duty of care extends to things over which the parents/coaches have no control ie weather/condition of the pitch/safety of the goal posts etc. You don't have parental responsibility for em mate. You can get around the "glasses" issue by telling the coach that the kid doesn't play unless the parent personally confirms with you that he's happy for them to be worn. That's all I do. If I don't get a thumbs-up from the coach and the parent - the kid won't play with them on.