Almost one in 10 five-year-olds in the UK owns a mobile phone, a study finds, with parents spending an average of £125 on their child's first phone.
The study, conducted by comparison site uSwitch.com also found that 42% of the 1,420 parents questioned do not pay close attention to the bills of their children's phones; parents taking part in the survey paid an average of £246 for their own phone.
Experts suggested that, while many phones were bought to ensure a child's safety, the devices were also being purchased to act as a babysitter to keep the child distracted on long journeys, and to stop them from commandeering their parents' phones.
Ernest Doku of USwitch said: "As well as arming kids with mobiles for emergencies and peace of mind, I'd imagine that many parents have bought their kids smartphones just to stop them commandeering their own when bored."
Nine percent of parents said they bought their child a mobile phone before they had turned five, while the average age at which a child receives its first phone was 11.
Almost all (97%) of parents said they did not disable the data connectivity of their child's phone, and so run the risk of the child racking up large data bills for accessing the internet and using social networks when not connected to a free Wi-Fi network. A quarter of parents capped their youngster's contracts so they could not overspend on calls and texts.
Doku suggested parents cap their children's mobile bills, adding: "Make sure that when they're at home, your kids are browsing the web using Wi-Fi instead of consuming data by connecting to the internet via 3G or 4G."
Another concern is children's ability to rack up huge bills from purchasing additional content for smartphone games and applications. Earlier this year, five-year-old Danny Kitchen charged more than £1,700 to his parents' credit card buying content for iOS game Zombies vs Ninjas, with some items costing £69.99 each.
The survey found that children aged 16 and under spend an average of £11 per month on their mobiles - less than the £19 spent on average by their parents. However, the research also found that 10% of children spend more each month than their mothers and fathers.