Regardless of whether DP and I chose to smack our children (we don't, but that's not the issue) nobody else would ever EVER be permitted to do so. For my child to think I *gave* permission to someone else to treat them in a way that makes them uncomfortable or upsets them gives me the shudders.

My Mum knows my take on discipline and is way too respectful of my parenting decisions to go against what I do. She smacked us as kids and occasionally smacks her own young child (not biological) and I don't say anything to her about that. That's her choice. I wouldn't smack her child, not even if she told me I could.

My MIL would be the more likely to smack but due to our history with her she has never been left alone with DD. With their current relationship she wouldn't, but only because she wouldn't dare cross us.

TBH this is the same as many, many things - what decisions are your parents/ILs able to make wrt what your children are fed, where they go, etc, etc. If they don't respect your position on parenting and realise what the boundaries are, how supportive are they to you and your family in general?