If someone is scatty enough to allow their child to open the door without supervision and damage another persons property then she should pay, she may not be so free and easy to let them do it again in the future as a result. I would not let anyone get away with damaging my property if it was their fault.
A few years ago one of previous Civic Type-R's was parked in my Mother in laws drive. Her drive is massive. It is literally wider than a couldersack. You could turn a large lorry around in it without hassle should you wish. However an ex girlfriend of my brother in law was unsure of being able to reverse her car and turning it around in the drive. She reversed straight in to the front of my car. Damaged and scraped the bumper. She came in to the house thinking that just mentioning she had hit a car in the drive was going to be enough to get away with it. I flipped big time at her, if she's incompetent enough to reverse straight in to my car then she can pay for the damage. My inlaws were protecting her a bit, but I thought to hell with it and tore shreds out of her for doing it. I have had comments about it from her, ever since the incident. But if she did it again I would tear more strips out of her. The fact is you have paid you hard earned money for the car. If someone else damages it they can pay for it, it's not your fault. IF you let them get away with it they will just keep on doing it as they have not learned their lesson.