Police say the two offenders, age 12 and 15, have been referred to Youth Aid.
"Police acknowledge the emotions of anger and resentment in the community towards the actions of these girls, and we would like to thank the public for their support and assistance with the investigation, Kapiti Mana area prevention manager Senior Sergeant Grant Ferguson said.
"I would ask the community to understand that the matter is now being dealt with appropriately, and the people involved need our support to enable them to change their behaviour.
"While we can't undo what has been done, we can collectively try to prevent this happening in the future.
"This incident highlights the fact that we still have a lot of work to do around how violence in the home and in our community can influence a young person's behaviour."
The organiser of the community festival said she feels disgusted that witnesses to the brawl filmed it instead of breaking it up.
"I'm disappointed that we have people in our society who have the sort of mentality that rather than helping somebody they would think that it's more important to film it," Liz Kelly said.
Kelly said the attack was the first in the 12 years she had managed the event.
She said what happened was really sad.
"My heart goes out to the victim and to her whanau but the actual incident had nothing to do with Creekfest.
"I've been told that this is a grievance between two families and they brought their grievance to Creekfest."
Porirua mayor Mike Tana said the brawl happened as people were leaving the festival.
It was out in the carparking space off to the side of the event.
"It did seem they were a group of young kids that knew each other and obviously something had happened and they were having an altercation that just didn't need to happen."