1.Keep it simple .A flag should be so simple a child can remember it. Two flags I think meet this criteria are Scotland and Tonga because they are simple.
2.Use meaningful symbols (icons,emblems) . for example- Kiwi,Koru,Stars,Moons and national emblems.
I think New Zealand and Fiji have meaningful symbols because there icons mean something. explain
3.Use three basic colors(strong)