I saw this movie 10-15 years ago and I remember it vaguely, so some points may be wrong.
A kid finds a rock in his front yard and, after a while, finds out that anyone touching the stone is turning into alien-like creatures, with bluish skin and long oval heads, with dark spots on them. In the end, I believe, everyone turned into "aliens" and they found out that there we're more of these rocks.
It might be some sort of series, as many episodes from several series where aired like movies here in Brazil.
I only want to find out which movie/series this is because it terrified me as a little boy and I think it was probably just an awful movie and not that scary.