2019 Toyota Highlander brakes problems

Me and my family were leaving a hotel in tarrytown ny. I parked the car: toyota highlander 2019 outside, helped my wife and 21-month baby into the back seat and had to put something in the trunk but it was locked. In that moment the car was in park with the engine running; the ground was not steep at all: 5-10 degrees the most. I took out the key from ignition to go open the trunk with the button from the remote. Suddenly the car started rolling backwards with my wife and kid in the back seat.

The contact owns a 2019 Toyota Highlander. The contact stated while parking the vehicle, the brake pedal was depressed and went to the floor; however, the vehicle failed to respond. There were several unknown warning lights illuminated. The contact turned off the vehicle to reduce forward motion and stop the vehicle. The vehicle was towed to the dealer for diagnostic testing however, the mechanic was unable to determine the cause of the failure.