Could it be The Ewok Adventure?
Wow. I think that might be it. Especially the bit at 0:07, with the giant chasing them through the mist. I really think that's it. Also, the sister and brother are familiar to my memory of this mystery movie, even though I've never seen Ewok Adventure before.
It's funny; it appears that my memory altered the movie a good deal, but I think that's it.
Thank you.