NZLARPS is sometimes asked about larp for young people. Most NZ larp events require attendees to be over 16, and permit young people to attend only with the presence of a parent or guardian. If you would like to run a larp for young people, we recommend the following:
Freeform Games has a number of theatre-style scenarios suitable for younger players, and has a page specifically about running larps for younger people. If you would prefer a free game, Down and Out in Middenburg and Graduation Day both have content suitable for young people.
For outdoor live-combat games, Claus Raasted of the Danish company Rollepsile Akademiet has a manual on Creating a kids' larp campaign. Larp is mass-entertainment for children in Denmark, so he probably knows what he's talking about.
Pay attention to safety. To help you with this, we have a FAQ on Basic Health & safety Compliance for Larps.
If you are in Auckland, KnightSchool does basic fighting training for children.