As reported in the New York Times and elsewhere, there were a number of incidents of teenagers getting into large fights at malls recently. Hopefully your children were not involved in any of them.
Interestingly, Washington State does not generally bar fighting in public statewide, as mentioned by this King County Bar Association article. However it still may fall under Disorderly Conduct and is also against some city codes, such as in Port Orchard and Pullman. In Seattle it's illegal to fight in public if it endangers others: "a substantial risk of [...] Injury to a person who is not actively participating in the fight; or [...] Damage to the property of a person who is not actively participating in the fight."
It also violates the usual posted rules of malls, and makes their continuing presence in the mall Trespassing, a private property owner can still make their own rules, within the bounds of the law.
However, this only applies to unarmed, fair "Mano a Mano" combat, not assault against an unwilling participant; and if a fight takes place at home, or between family members, Domestic Violence law applies.