As has been recently covered in NZ news outlets, the issues facing US citizen children with KiwiSaver can be significant, but resolvable.
US Global Tax currently has a petition sitting with Parliament to change KiwiSaver rules, to permit under-18 US citizen children to close KiwiSaver early. You may sign the petition at https://www.parliament.nz/en/pb/petitions/document/PET_127472/petition-of-david-tzimenakis-adjust-the-kiwisaver-act
Learn more below: