Here's an excerpt provided by an actual user:

I'm standing on the vast southern lawn at Ashton Court, a stately home on the edge of Bristol, clutching a tiny electronic machine that mimics Adams's device quite eerily.

It's the size of a postcard and has a small colour television screen with earphones snaking to a slot in the bottom. When I walk a few yards to my right... ping! A bell shrills in my ear and the screen bursts into life.

A cheery voice declares, "You have walked into an interactive area." And what begins is a visitor experience like no other I've had. This tiny electronic prototype, called an Explorer, detects exactly where I'm standing within the 850-acre parkland surrounding Ashton Court, because it's equipped with an internal Global Positioning System (GPS) based on satellite signals, accurate to within about three yards.

On screen, I see myself as a little red dot moving slowly over the grass. Depending on where I wander, an entirely different heritage or cultural story is presented through a combination of pictures, sound effects and narrative, all related to where I'm standing and what I'm looking at.

I walk to the bottom of the lawn. Ping! With the sweeping façade of Ashton Court spread like a film set, the screen shows me how the building has changed over the centuries, images building upon images as a voiceover explains why the place looks as it does now.
(From Travel Gadgets: it knows where you are)

(From Node Explorer V3 Profile)

In his 1979 novel Hitchhiker's Guide to the Galaxy, Douglas Adams describes the guide this way:

"I'll show you how it works," said Ford. He snatched it from Arthur who was still holding it as if it was a two-week-dead lark and pulled it out of its cover.

"You press this button here you see and the screen lights up giving you the index."

A screen, about three inches by four, lit up and characters began to flicker across the surface.

"You want to know about Vogons, so I enter that name so." His fingers tapped some more keys. "And there we are."

The words Vogon Constructor Fleets flared in green across the screen.

Ford pressed a large red button at the bottom of the screen and words began to undulate across it. At the same time, the book began to speak the entry as well in a still quiet measured voice.
(Read more about the Hitchhiker's Guide)

Although I usually stick to science and science fiction, I can't resist adding the reference to Harry Potter and the Prisoner of Azkaban. Fred and George Weasley present Harry with the Marauder's Map, a remarkably detailed map of Hogwarts castle with the following amazing feature: a little dot represents the location of every person in the castle:

But the truly remarkable thing were the tiny ink dots moving around on it, each labeled with a name in miniscule writing. Astounded, Harry bent over it. A labeled dot in the top left corner showed that Professor Dumbledore was pacing his study...
(From Harry Potter and the Prisoner of Azkaban)

Wouldn't it be handy if each person in your party had their own device, and you could see everyone's location in your device? Definitely parent-approved.