Name of this CHILD HORROR MOVIE?

It's winter/snowing and a couple of families and their children are in
one house, I think a girl child turns evil and kills people then her
brother turns evil.

I remember a tent in the garden where one of this children drags a
body - I think, and at the end of the movie their mother runs them
over in her truck...

Seen it few years ago, just can't remember the name, it's a sort of
modern movie.