The small black stones....

There's about 199 unresolved issues about this shoddy piece of work, and you just picked up on one of them.
That being said, I'm sure someone on here will provide a satisfying answer for you

I think they were mainly meant to add mystery, but the tie in was that they were at the location where the spaceship would pick up the children.

The stones meant the children were chosen for the journey ahead.

Alien business cards.


The players of The Game are the scum of the earth

Alien petrified poop

Nibbler poop, it is used as fuel for their ship.

You're adopted!

Well, it looks to me like some vulcanic stone, for the signifcance I can only speculate as the poster before me, that they are ment as sort of a ticket...

I think its the stones form the landing spot.
It was supposed to be a clue as to where to go to be saved, that and the numbers.
But when people ended up being too thick to get that the aliens came and drove them by a car .. literally to the spot they should be in.
So basically just a business card fro this particular ship, my guess is other ships left different clues.