I remember seeing this film maybe 20 years ago, saw it on TV so it will be even older.
It was set in the future in some sort of post nuclear war type era. Water was in very short supply. It followed a group of kids on rollerskates, there didn't seem to be any adults. The kids found some sort of special golden orb/ball/alien that they kept in a rucksack and set off on a journey with this thing to take it somewhere important. People were chasing them so they were always having to skate fast to escape.