A New Zealand Future: Ged Maybury, Time Twister (Auckland: Ashton Scholastic, 1986).
In Time Twister Troy, Helena and Jason are drawn to a computer arcade game that lets them into the past and future. Once they are hooked, they are drawn into the future by the mysterious figure[s] of Yos who shows them how to use the helmet to go back in time and change the future so that the world is not enslaved by a computer corporation.
A number of things make the book unsually interesting: although Maybury explains too much, it's usually after the event rather than before, which makes me wonder if an editor demanded "clarity", and there are plenty of occasions when we are left to work it out for ourselves.
Troy, the eldest boy, has such a bad first experience that he doesn't travel again, and tries to hand the adventure to his younger brother Jason--warning his sister off the dangerous mission. But as it turns out, Jason and Helena have different aspects of the Gift. She can handle the time travel far better than he. What Yos wants Jason for is his computer skills.
The depiction of early computer programming (the mainframe is programmed with a tape) is done very well, and particularly good is the way Jason and Helena think themselves around the time problems. Less convincing, but endemic to adventure fiction generally, is there assumption that Yos are the good guys (just because a foreman is a nasty piece of work, surely doesn't necessarily damn his entire company?) Maybury cheats by giving us one--and only one--glimpse of the company plotting against the family's father, but it is a necessary cheat which helps to undercut this irritating trope.
Yos, by the way, means "Your Future Self".