any technology allows shopping malls, theme parks etc. to track identity of...

...visitors through mobile phone? I am studying about this area and would like what the existing technologies available to track the identity of the visitors in an area, do not have to be location of them, it can be as simple as status of entry and exit. Preferably I want to know any visitor tracking are done through mobile phone.

For example, Legoland uses WIFI to track the location of the children who holds a special ID tag. Any similar technologies implemented for mobile phone?

Your suggestion would be a violation of a persons privacy at a minimum. Currently the cell phones sold in the USA have E-911 capability which will allow the phone location to be tracked within a couple feet for its location by some highly equipped emergency services as long as the locater is turned on and the phone is in a covered area of the country. It was made into law a few years ago when a few children died in the NY harbor after calling 911 and 911 could not locate and respond to them fast enough.

As far as releasing their identity to the public that is a security risk in its own right.

It's theoretically possible to track presence (but not identity) of mobile phones as they communicate with the cell towers, but because you can't identify a specific mobile phone within an area, it's "tracking" abilities are limited (keep in mind that because the cell phone companies own the towers in question, they CAN track individual phones). A much easier implementation for a theme park or etc would be to simply use some sort of long-range RFID tag (embedded into a ticket or wrist band or similar) with sensors around the area to be monitored.