Whenever I hear another mother say her teenager “tells her everything”, my knee- jerk reaction is to think guiltily: “Where did I go wrong?” But that’s quickly followed by wondering if she is deluded.

Those occasions when you wanted the incessant, head-wrecking chatter of a four-year-old to stop seem a lifetime away when you find yourself trying to extract slivers of information from that same child 10 years later.

In my limited experience, teenagers like to operate strictly on a “need-to- know” basis with parents. But their definition of “need” is at odds with ours – for them it might be so they can get a lift; for us it’s wanting to know where they are, who they’re with and when they will be back, so we have at least a sketchy idea of what they might be up to.

As for the bits in between, that’s their business – unless there’s a problem – and no matter how curious we might be, we’re probably better off not knowing.

Clinical child psychologist and mother of teenagers Sarah O’Doherty concurs, describing teenagers as “innately secret”.

“The minute a child or a mother says that the other is their best friend and they tell them everything, the alarm bell goes. You are meant to have secrets as a teenager – it is part of your development and separation from your parents that you learn to do things in a different way to them,” she says. “It is not appropriate to be constantly guided by your parents’ attitudes and views.”

She knows women who are so close to their daughters that if a boy texts the teenager, mother and daughter will sit down and work out the response together. There are no secrets between them.

“If you are a mother you cannot impose boundaries and rules if your child is your best friend and you have no safe secrets.”

As with younger children, the crunch is where the line is drawn between safe and unsafe secrets among teenagers.

“Secrets between friends at this stage can become quite big, quite dangerous,” O’Doherty acknowledges.

Perhaps it’s an eating disorder, a controlling, older boyfriend or drug experimentation. Disclosure might be in a friend’s best interests but teenagers sworn to secrecy won’t want to say anything. Yet keeping it quiet can be a burden.

She is aware of an instance where a girl who had been sexually assaulted would not tell her parents but confided in her close friends. However, they didn’t feel they could tell anyone outside their circle – until one eventually told her own mother.

In such circumstances, parents need to think have they created an environment where their child can come to them, O’Doherty suggests. “It’s a tricky, tricky balance.”

As a teenager, she recalls herself and friends giving parents a broad outline of what they were doing but never lying. Whereas another friend felt she could never tell her parents the truth about what she was doing because they were so strict.

“I think that idea of being secretive and being sneaky comes out when parents are overly strict or disapproving, or make their views so black and white there is no room for the child to put their own viewpoint forward,” says O’Doherty.

She is "completely against" the idea of checking teenagers' Facebook pages and phones, unless there is a cause for concern.

“When they’re seven or eight I think it’s all right to casually glance at them but I have told my children I will check your phone and Facebook only if I am worried about you.”

However, she has always advised them when writing in social media to imagine somebody else is watching and that everybody will read it.

Generally you are better off not knowing what your teenager is doing on Facebook or on the phone, she adds, unless the child is very immature or there is a specific worry.

“What they are saying is not designed for their parents to read – they are different people when they are with their friends and online. It is mortifying for them.”

Teenagers are entitled to use social media without parental surveillance if they have earned that trust, says Colman Noctor, child and adolescent psychotherapist with St Patrick's Mental Health Services in Dublin.

When it comes to social media, he believes a parent’s starting point has to be access to everything and then to step back gradually – not only as children get older but “as they show an ability and common sense in that space”.

There are some 12-year-olds you would have no problem with having access to social media, whereas there are some 17- year-olds you would have grave concern about, he points out. But generally he believes parents need to keep a watchful eye on the online activity of teenagers still in the junior cycle of secondary school.