"We offer a GPS-enabled service which allows families to locate a child or other family member using a PC, laptop or compatible phone," Laura Porter of US cellphone company, Sprint, told AFP on Monday, just days before some 36 million American children are expected to go trick or treating for Halloween.
Another cellphone company, Verizon, offers a similar service to its subscribers.
"The Chaperone Parent provides a way for you to determine the location of your child's phone from the internet or from a phone," Verizon spokesperson Brenda Raney said.
"There's also a service where you can create parameters and if your child goes outside of those parameters, you and the child will get a text message," she said.
A big fear at Halloween is that children – some of whom go trick or treating without an adult – will inadvertently call at the home of a sex offender.
Sprint has teamed up with familywatchdog.us, which has mapped the home and work addresses of registered sex offenders in all 50 states, to try to allay that fear.
"Parents can set up text alerts to be notified when a registered sex offender moves to or from their neighbourhood. They can see if there's someone within their home or daycare area who is a registered sex offender," Porter said.
Americans also have access to a public, internet-based registry, set up by the Department of Justice, which lists the addresses of sex offenders in all 50 states.
And many states require registered sex offenders to report to the local police station or their probation office during peak trick or treat hours, to avoid contact with children.