I would have no problem with it if it was reasonable and done in a respectful manner towards my child. I would be horrified if another person took it upon themselves to smack my child as i do not do it myself.

I do believe that it can be a good thing for children to learn discipline and different boundries from various adults in various souroundings.

If i am ever in the situation where something needs to be said to settle children down a little or change their game as it is something i don't approve of in my house i will say something but i will do it so as all involved are being spoken to and not singling out anyone in particular.

Once my children were at a family get together with my DH and i was not there. DH came home and told me that my newphew (how can be a bit of a cheeky one to put it nicely) decided to just pull my DS1's pants down in the middle of the room with no motivation at all, DS was 4 and nephew was 6. I was so horrified when DH told me, he said that he mentioned it to the parents and they just laughed it off but my gosh if i was there i don't know what i would have done. I would never have touched the child obviously but i would make it quite clear (with everyone watching if that was the case) that he is never to do that to my child ever again. So yes in an insatance like that especially if the parenst are going to do nothing about it i would say something.

I'm doing my best to bring up my childred as well mannered and respectful human beings.