Every effort has been taken by phone manufacturers to make mobiles so simple that a child could use them. However, as many a parent has found after their child has grabbed the phone, punched in a few numbers and started an unwanted, expensive phone call to Algeria or points beyond, some of the devices are now too easy for children to use.
But parents don't need to resign themselves to letting their kids rack up long-distance minutes.
Some basic tips - some as basic as hiding the telephone icon on your phone's screen - should keep the unplanned telephoning at a minimum.
"You can block your telephone with a security code or with its fingerprint sensor," notes Monika Klein of German computer magazine Connect.
But setting up that kind of protection also means children won't be able to access movies or games that they're allowed to use and see.
The three largest platforms - Android, iOS and Windows Phone - offer no option to just block access to the phone app.
Still, this does not mean parents are helpless.
"You can hide the telephone icon in a folder," advises Klein, noting this will generally flummox smaller children.
Another option is turning on airplane mode, which cuts off all telephone and data communications. Of course, going this route also means blocking any incoming phone calls and emails.
One longer-term solution is to block access to certain kinds of telephone numbers.
"In many nations, international numbers and premium numbers can be blocked by your service provider," says Falko Hansen of German telecommunications website teltarif.de.
However, once you go this route, it means the block has to be deactivated as soon as you have to make a call to one of those numbers.
Frustrated parents should also consider one of a variety of apps out there that can block access to certain parts of the phone, or others that only allow outgoing calls once a password is entered. However, user reviews of such services have been mixed.
Users of Windows Phone 8 and more advanced devices can make use of a mode called Kid's Corner, which sets up a special area children can access to reach their games and apps, but which blocks them from the phone and sensitive data.
Internet access is very limited here in Kid's Corner and online shopping is blocked.
"If a playing child has access to the smartphone, it's recommended to set up password protection for the app store," advises Hansen. Otherwise, you risk an even bigger unwanted bill.