Curfew for minors in a private business but its open to the public?

While my daughter was at her dads for the week they dropped our 11 year old off with her 12 year old step sister to a gym at 11PM at night till 1:30AM. The 12 year old scanned her mothers pass making the gym think she was a 32 year old woman and my daughter used the 12 year olds gym membership. When we told them thats illegal and no child should be out that late they responded with "its not illegal since its a private business". This happened in Rancho Cordova CA which states minors are not supposed to be out passed 10PM even at food locations like in n out without supervision.