The low voltage battery went out after rear right door was opened to put children in car seats. Drove 45 minutes to a train museum with the kids. Everything was working fine on the way down. Once done with the museum and back at the car, opened right rear door to put my younger child in the car seat. My older child decided to enter the car through same door as she didn’t want to wait for me to finish to take her to the other side. Once my younger child was buckled up, I closed the door to come over to the other side the buckle in my older child into car seat. The door would not open. The phone application would not get the car to unlock the doors. I could not open any of the doors. Children were trapped inside. My oldest child was not yet buckled and I was able to instruct her to crawl to the front and try opening both doors with the electronic button, which did not work. I then instructed her to use the mechanical door latch vs the electronic and she got the door open. Had it not been for the fact that she was still unbuckled she would not have been able to get to the front to open the doors. I would have needed to call 911 for help getting the kids out as the car was unresponsive.