It sounds like you have come to a good resolution of this, and that is an important outcome that may prevent future problems.

I did not communicate something very well. In no way do I believe that parents should give in to other peoples' judgement about what to do when they are caring for a child. I would have a hard time giving over the care of a child to someone who would disregard clear instructions. Like you, I would expect wishes to be respected. I'm glad that your mother has accepted your position on what happened. This is a safety issue. On safety there can be no compromise. Your judgement about what is too risky for your son should be final.