More than a million British children have their own mobile phone by their fifth birthday, according to new research from uSwitch.com.
On average, children get their first mobile around the age of 12 and parents spend £125 on the handsets, compared to £246 on their own. But the firm also said that almost one in ten (9%) children have a handset by the age of five.
Parents spend around 15% more on their first-born's handset than they do on their second child's phone, the research showed. But 11% of under-16s have more expensive phones than their parents.
Four in 10 parents don't monitor their children's mobile bills, while just 25% cap their kids' contracts and just 3% disable the data function on their children's phones so they are only able to use them to call and text.
Kids' phone bills are £11 a month on average, less than the £19 their parents spend; although, the firm added that 11% of children rack up higher bills than their mums and dads.
Ernest Doku, telecoms expert at uSwitch.com, says: "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.
"So if you do give in to your kids' requests, asking networks to place caps on their mobile bills takes about five minutes and is a very sensible precaution, especially if your child has a data-hungry smartphone.
"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."