A second reporter and the girl's mother were shot and injured by the same gunman, who is also suspected of the other homicide, police say.
The two Spectrum News 13 journalists were covering the killing of a woman in the area that morning when the teenage suspect returned, police say.
It is unclear if they were targeted. sa casino
The suspect was armed when he was arrested and was not co-operating with police, said investigators.
None of the three people killed in Wednesday's two attacks in Pine Hills, a suburb west of Orlando, has yet been identified.
In a news conference, Orange County Sheriff John Mina said the journalists were "in or near their vehicle", which he said did not look like a TV station's official vehicle, when they were attacked at around 16:00 local time (22:00 GMT).