Bec if it was me..and ive actually been in a similar situation, i would just keep reiterating (maybe a little louder!) what you do with your darling smee. Sounds like you are giving mum all the verbal and non verbal cues already..keep them coming, they are bound to sink in..other than that, hope that she is perhaps a little bit over the group and will find something else for her little boy to do, rather than interfere with the safety of the other little littlies there.

Sorry..posted at the same time. Given mums background, it does put a different spin on it. Its hard sometimes to see our own kids not as an extension of ourselves, but little people in their own right..for her, it might be completely reasonable to be acting this way in protecting her son( her own inner child)
Jo