I think it could be Australian/Polish co-production Spellbinder (1995).
While at summer camp, Paul Reynolds accidentally goes into a parallel universe. This other world is inhabited by a more hierarchic and technologically different society, ruled by a group of people known as Spellbinders. Paul meets a girl there named Riana, and they become friends. The Spellbinders have discovered the power to create and manipulate static electricity. They fly in gigantic copper-coloured machines that utilise large rotating orange crystals, presumably creating some form of magnetic levitation. The Spellbinders often use their power for good, but some abuse this power and use their discoveries for malevolence. One such malevolent Spellbinder is Ashka, who often manages to hide her true nature. Common people are often "banished" for their misdeeds, and sometimes Spellbinders are banished, also, if they are proven to have done wrong.
It has a sequel, Spellbinder: Land of the Dragon Lord (1997).
It has the boy and older/taller girl (see picture) and strong science fantasy elements. I don't remember the colorful creatures, and I'm not sure about the wooden bridge over a chasm. It has, however, been 20+ years since I saw it.