Loved Fiji but we stayed at a lovely resort on the Coral Coast and just chilled. We went to a village (by kayaks!) one day which was great and we also went to the markets in Sigatoka. Other than that we took it easy. Not much help, I know, but boy it was nice!

My advice with kids, find a good resort with a great kids club and a family friendly swimming pool. If you don't mind moving around, maybe split your holiday so you try out one of the islands and then the mainland too. Avoid Nadi, it's just a hub to arrive and depart. The family friendly resorts offer awesome tours and activities for all ages.