Bushwalking in Fiji?

It's only a half serious question. We're flying to Nadi tomorrow and spending 10 days at a resort on the Coral Coast with my wife's brother's family. They have 4 kids aged between 1 and 8. For my own sanity I may need to escape from our rugrat nephews and niece occasionally. Has anyone done any bushwalking around that part of Fiji? I'll only be equipped for short day trips at best and need to use public transport. What about the heat/humidity, or any other issues?