Children as young as eight-years-old have their own smartphones

Experts say that peer pressure, fun games and apps and they ability to stay in constant touch with their friends means that smartphones are now seen as a must-have by all age groups.

But there have been warnings that parents to be careful when handing their child their first phone, which can open up a window for online bullying and unwanted interactions.

And the tech-savvy youngster's mobile phone habits have led to some shock bills for their parents, according consumers groups.

A survey of children aged eight to 15 years old found two-thirds (67 per cent) have their own smartphone, rising from 19 per cent of eight-year-olds to 95 per cent of children aged 15.

Almost nine out of ten parents said they foot the bill for their child's phone, rather than their offspring having to pay out of their own money, according to the findings from the Halifax Pocket Money Survey.

The probe found that many children's phone habits are unregulated, with two-fifths (40 per cent) claiming they are allowed to download as many apps as they like.

This is despite some programmes coming with hidden costs and in-game shops which can be accessed with a single flick of a finger, causing some unwitting youngsters to spend hundreds.

Citizens Advice said it helped one parent hit with a mobile phone bill of over £300 after their 12-year-old son signed up to a games app.

The charity also helped another parent who found himself paying for an £80 year-long subscription to an app that his daughter had downloaded, thinking it was free.

An investigation by consumer help website MoneySavingExpert.com in 2015 also found in-game extras could cost as much as £80.

Halifax's survey found that children potentially spend nearly £500 (£487.24) of pocket money a year on digital downloads.

When Halifax asked children in its survey where they think money comes from, one child said: "Money doesn't actually really exist as it's just numbers on screen really."

When a child's mobile phone use calls for parental intervention, Halifax said that mothers are more likely to put a stop their children's downloading habits than fathers.

If children really want something, nearly half (45 per cent) said they would ask for it as a birthday or Christmas present, while a fifth (19 per cent) would use pester power until their parents gave in.

A third (28 per cent) would save their pocket money until they could afford it.

Ministers have recently decided to step in and help parents ensure their children use smartphones responsibly  the Digital Economy Bill received Royal Assent.

The Bill aims to help protect consumers from a "bill shock" by requiring mobile network operators to offer a bill capping facility.

Regulator Ofcom suggests parents buying a mobile for their child should consider what type of device they need, and if a basic handset would do.

Previously, Child psychologist Dr David Lewis warned that smartphones were an "electronic tribal drum" children use to keep up with their peer group

'The mobile now often substitutes for physical play,' he explained.

'To develop proper friendships you have to invest time with people, doing things together.

'Speaking on the phone and sending lots of text messages will give children many more acquaintances but fewer friends. They are replacing quality with quantity.'

Giles Martin, head of savings at Halifax, said: "With more and more games, apps and music offered on smartphones, digital downloads are naturally becoming increasingly popular for kids to spend pocket money on.

"Although each download may seem fairly cheap, the costs can add up over the course of the year and their lack of 'physical' presence can make spending less visible.

"Parents could use this opportunity to spell out to their children how small amounts add up."

Tech expert: Smartphones bring both benefits and dangers for children.

They have become the must-have gadgets for both parents and children, both a incredibly efficient way to stay in touch and an insidious way to fritter away free time.

Smartphones place the entirety of the digital world in people's pockets through their ubiquitous apps, games social media platforms, and keeping track of what's hot and what's not in the ever changing world of childhood fads can be a full time job for a parent.

And while there are hidden costs and pitfalls with giving a child a smartphone, experts say the devices have their place in their school bags if they are used responsibly. 

Ben Cook, is Marketing Director at social media consultancy JC Social Media, explains: "Smartphones bring the world to a child's fingertips. They're not just tools to use in an emergency or to arrange a lift back from a friend's house.

"The array of games and apps available means the smartphone is a constant source of entertainment for kids, especially young children.

"If anything, giving them a smartphone is freeing up time on mummy or daddy's iPad. Whilst it seems crazy that we're giving children as young as eight iPhones children have been playing on things like Gamboys for decades.

"They've been using the internet and personal computers for years too. The smartphone just happens to be all these things in one! Arguably, it's a natural evolution driven by technological development rather than cultural change.

"It's unsurprising that 1 in 5 eight-year-olds now have a smartphone. We need to remember how cheap smartphones have become; they're now free with very basic phone contracts.

"If you're going to give your child their first phone, why not make it a smartphone? Peer pressure amongst children and parents obviously adds to all this. Getting one's first iPhone is almost becoming one of life's significant milestones like getting one's first car.

"As a parent, you're always going to give your child the best you can and if the parents around you are getting their children smartphones, you're likely to follow suit.

"Social media creates a huge amount of social pressure, especially for children. Social media use is being increasingly linked to mental health issues, especially Instagram.

"Whilst most platforms have a minimum age, parents should be aware that the age checks are anything but stringent.

"Given all the evidence, parents should monitor the apps on their children's phone to ensure they're not using social networks before they're allowed - the age restrictions are in place for a reason.

"Even if their children are of age, parents should look out for changes in mood or behaviour that could indicate they're being bullied online.

"More than a quarter of adolescents report having been repeatedly bullied via their phones or on social media and more than half do not tell their parents about it. "Parents need to encourage children to get out and meet their friends and take up activities in the real world.

"We shouldn't be against technology and the largely positive changes it brings, but we must be mindful that we don't yet know the full extent of living one's early years on a smartphone and social media."