According to the latest episode of 'Threshold', the aliens may have been to Earth as long ago as a century before what was considered the initial contact on September 16th, 2005. This was based on the discovery of a 4-dimensional artifact of alien origin that had been found buried in Ohio, and analysis of the surrounding dirt.
Having been there since at least 1900, it's now a possibility that its mutagenic powers might have seeped into local water tables. Or perhaps it passed its deadly traits through the food chain via local crops. Buried as it was, it was theorized that its power had been dampened. But even so, over an extended period of exposure a family might have found itself affected; it may not have been readily apparent, but it still could have manifested istelf in future generations through DNA.
So it's possible this is the reason why Anthony Fremont was born in Peaksville, Ohio, already exhibiting the deadly powers he would use to isolate and terrorize the town by the time he was eight years old. ('The Twilight Zone' - "It's A Good Life")
Anthony might have also been part of the family tree that could be traced back to the demi-god Evander ('Hercules: The Legendary Journeys' - ""), all of whom were able to bring their imaginations to life.
And even then, the addition of the alien energies to his genetic make-up would have augmented the danger Anthony Fremont posed to the world with his "wet, purple gaze".
But... that's a good thing. It's a good thing that it happened. It has to be - I don't want to be wished into the corn field.
Or didn't you ever wonder why Martha Stewart is always saying it's a good thing?