The myth of Merlin given the kids movie treatment.
Glancing over the cast list should give you an idea of how misconceived this whole project is. As Arthur (Bergin!) and his knights face their final battle with Mordred (Sheffer!!), Merlin (Mayall!!!!) locks them in the underworld until such time as the battle will end on the side of right.
Flash forward to the dawn of the 21st century, and an evil scientist (Carrere - for whom exclamation marks are not enough) has contacted Mordred through a psychic hoping to bring him back to full power. Two kids team up with Merlin to fight the baddies and get involved in some sub-plots that make NO SENSE AT ALL.
All the budget clearly went on the spooky ghost effects that pop up half-way through the movie and do little to save it.
Unless you're between the ages of seven and nine, you'll lose interest long before the end.