Really wanna know the name of a film i used to watch as a kid!?

It's really buggin me, cos i can remember little flashes but not the general plot. I think it involved sum kids who went to sumthin along the lines of a science lab or computer game factory and got stuck in another dimension, or inside a computer game, or, well, sumthin along those lines. I can remember one of the girls was blonde with gles and scd her knee..I can also remember a scene where they had to cross a lake or a swamp by going over what looked lik a giant upturned spine. ther may hav been dinosaurs in the film, and im sure ther was a pit filling up with lava that continued to fill up throughout the film...sorry the details are so sketchy, i jst remember rly likin this film and i wna watch it again. it was late 80s, early 90s i think. if any1 thinks of a film tht broadly fits tht definition help me out! much appreciated