From what I remember of the movie, there were these two "villains" in red and yellow suits that looked like something from power rangers. The kids ended up in a place/dimension that looked like a cave, that had this small person working there who was hostile to them at first, but they then made friends with it.
It was later revealed that the power suits were built by the little person, and the two villains were in fact older versions of the kids, the boy being in the red suit and the girl in the yellow. The "villains" were in fact just there to make the kids behave in a way that would lead to the future they were living in currently. The kids grow up to marry each other.
The younger version of the girl kicked the red-suited older version of the boy in the groin when they were being chased, for which the older version of the girl apologised to the boy later on.