I remember seeing this one a long time ago, but all I can remember is the beginning. Two kids, I think brother and sister... I think they had one of those old rope swings with the wooden seat, because I remember them playing on it, and then running off to play in the woods and something bad happens that sets them out on their journey. (I think one of them gets captured maybe?) I'm pretty sure it had elves or trolls or something of the sort in it. I know that's not very specific, but any suggestions to what it might be would be appreciated, thanks.

Sounds so familiar!