An ex-con taxi driver in Las Vegas takes two blonde kids miles into the desert because they are paying him with a wad of cash. On the way they are followed by government agents, who know the kids are really aliens. However, he thinks these cars belong to his old boss--and that he's trying to scare him back into working for him. He doesn't want to go back to jail so he's on the straight and narrow.
The boy can control his molecular density and the girl can levitate objects with her mind, which provide an excuse for some special effects. There is also an alien soldier after the siblings, which the cab driver is able to protect them from.
There are also cameos by the original stars of ESCAPE TO WITCH MOUNTAIN (1975), Kim Richards and Ike Eisenmann. They are in a bar scene in which she's a waitress and he's a sheriff. While it was good to see them it is somewhat jolting to see how much they've aged in the past 35 years.
Basically, everything in this movie is doubled up from the original. There are two evil factions after the kids and if either capture them the earth will be invaded by an alien planet. All this convolution only bored me--and made me want to re-watch the original.