I wouldnt recommend Fiji for beginners going without boat support to get away from coral reefs.
Can you stay upwind, if you cant and you kite 100m out from a resort and get into difficulty it will not end nicely if getting dragged downwind over coral

At most of the resorts on the coral coast you can prety much forget kiting a couple of hours either side of low tide.
There are not really any nice sandy bottom flat water spots located at any of the resorts that will have child minding facilities.
Fiji is surrounded by coral reef, there are not that many nice sandy beaches
If you are getting dragged anywhere you will come home with coral cuts everywhere.
I here Cocos and Cook islands have nice sandy lagoons
Have you considered north qld, perhaps port Douglas would be good
Dont forget to do a search on here for fiji, there has been heaps written before

No kite shop in Fiji, so take everything you need, cant even buy a harness there