How times have changed. The general consensus from today's parents about anyone itching to tell a child off who isn't their own is to bite your lip. Hard.
"I am his mum, and I will discipline him in my own way," ranted one mother recently on one of many online discussions on the topic. "My son is only five, the same age as her son, and he may not be perfectly behaved, but neither is her boy and I wouldn't dream of telling him off."
There are hundreds more comments like this – and for many parents, it's not just strangers they don't like disciplining their children.
"I love my best friend, but she's so protective of her children that we can no longer holiday with them," says Rachel Appleby, a mother of two from Somerset.
"The first time we tried it, our kids were all aged two to four and more than once, she asked me not to 'chastise' her kids. On the second holiday, a year later, we wound up having a massive row when I told her son off. It's wound up affecting our friendship and I just don't get it."
In some cases, even the child's grandparents are discouraged from condemning any misbehaviour. And we all know at least one parent who seems to march into the classroom every time he or she feel the teacher has been unduly harsh with their darling cherub.
The notion that only a child's own parents should tell them off is a relatively recent phenomenon, says Rebecca Chicot, an expert in child development and parenting and founder of the Essential Parent Company.
There's an old African proverb that says 'it takes a whole village to raise a child' and certainly, that's the approach we used to take towards child rearing. But this has all but disappeared as people live increasingly private lives, feeling utterly responsible for their children, for good or bad.
Part of the trend away from public family life is down to there being less playing in public spaces, such as local streets and fields, she says. We also drive more, so there's less interaction with other families on, say, the school run, or just walking to get groceries. We are less likely to know our neighbours and we are more likely to be suspicious of strangers, especially those who speak to our children.
"Parents are more informed about child development and this is also relevant because it means they often have very fixed ideas about parenting," says Chicot.
"In the past, families just got on with it but now, every single aspect of parenting is analysed and picked apart, whether on TV, in parenting books or online forums. So whether it's breastfeeding, controlled crying or how much chocolate your child is allowed, we accept that each family has their 'way' and that's not to be interfered with."
But, like most parenting experts, Chicot is all for allowing your kids to be told off by others.
It's not good for a child's development to see adults watching their unacceptable behaviour and doing nothing about it. It gives them mixed messages about right and wrong.
"Being told off by other adults when necessary is also helpful in building up resilience and preparing them for the big wide world – a world, that when they're adult, does involve different people getting loud, bossy or cross."
Chicot herself certainly gets stuck in when she needs to. "I do encourage other people's children to stop certain behaviours, such as dropping litter, and I'll also – for example in a playground situation – step in when the child's parents are there but perhaps not attending to a situation that is dangerous or where a child is being bullied. Equally, I'm accepting of the fact other adults will sometimes need to be firm with my children when I'm not the 'first responder' or haven't noticed a situation."
But, she says, this comes with caveats. "For example, I believe that if you're prepared to tell other children off, you must also be willing to comfort them. The two go together as part of your responsibility in the public sphere. I'm also careful about how I tell children off - never doing it in a confrontational way or trying to show up the parent."
Child development expert Dr Amanda Gummer agrees. "In fact, I think one of the main reasons parents don't like other people telling their children off is that they take it as personal criticism. There's so much pressure on parents to 'get it right' now that they are the ones who feel upset if their child is reprimanded, even if it's by a close friend or relative. I don't tell other people's kids off in front of their parents if possible, although I do if it's serious enough."
When her kids' friends come round to play, Gummer treats them just as her own, however. "Kids need consistency and boundaries and if you suddenly have a different set of rules for other children in your house, what's that saying about the importance of those? I'd have serious problems enforcing rules such as table manners with my two if I allowed other kids to get up and down from the table willy nilly, for example."
But again, she says there's a right and wrong way of going about this. "It helps to explain the reason for the rule. Also, there's a big difference between saying, 'Please don't do x,' and 'What on earth do you think you're doing? That's very silly indeed!'"
Clinical child psychologist Angharad Rudkin believes parents should just chill out.
"There's a preciousness around parenting that wasn't there in the past. We see parenting as a career – so if we are good parents, we are doing well in the world.
"But the truth is, your child will misbehave sometimes – that's just how it is – and you won't always be there. If someone else can help give them the right messages about that behaviour, it will ultimately make you and your child's journey that bit easier. In other words, don't sweat the small stuff."
In any case, as Chilcot points out, disapproving looks – the substitute that many adults use instead of a good old-fashioned telling off – is no more constructive.
"That's worse than anything and I just can't fathom why a person would think it's more respectful to give anyone an evil stare and look disgusted by the situation than to try and diffuse the situation by communicating."
What do you think? Have you told children, not your own, to behave?