will someone please, please explain the beginning of this movie to me

Bump witches bump!

The opening scene is set in California in a house where the mother/son have had to quickly flee as their exploits began to become apparent in the town. In that scene, 2 cops go into a house after finding the outside of it littered with strung up dead cats. Most likely the cats are the product of a previous battle between them and the Sleepwalkers. The police find the corpse of a dead girl in a closet of the home with a rose in her ear illustrating the mother/son's motus operandi.

This short scene illustrates the evolution of the sleepwalkers' cycle, meaning many dead cats and virginal corpses left behind. In the opening credits we see various historical artifacts showing a fractured chronology of exploits of Sleepwalkers throughout the ages with the first dating them back to Ancient Egyptian times. To me, the deliberate juxaposition inferred that they are either decendents of Bast and/or Sekhmet (the Egyptian Cat Goddesses) that fell from grace or that they belong to a race that are the supernatual nemesis of Bast and/or Sekhmet. When we next we see the mother/son couple, they are in Indiana, seeming to start off anew at this point and looking for new prey to feed.

Hope that helped. If you have any other questions feel free to ask.