By dumping their feelings on OP, the neighbours are inviting people to look critically at why their son had an accident in the road in the first place.
I'm by no means a Freudian kind of Psychologist or Analyst but I do think there's a lot in the theory of projection. People who are feeling something badly like guilt or shame or regret project it onto someone whom they find is the easiest person to attack and onto whom these feelings will stick most easily.
This is a classic case, the neighbours know their son was unsupervised, on the road and exposed to danger when they were not watching over him and he had an accident. Then they discover that the person whose door they knocked did not answer them! They're not interested in being reasonable or logical. They jump straight away on someone they can attack for what they can frame as being negligent. They can project all their own fears about not bothering to go outside and watch over their child and keep him off the road, all their guilt about him being there alone, and their anger that he had an accident and showed them up for being negligent parents. Now they can blame someone else!!
Projection always comes with anger. They want to point the finger at you. In this situation you need to take a step back. Think. Are you responsible for their feelings, or their lives, or what has happened? They love to say things like you are crazy or selfish so if you do not have a happy sense of self you may take on their projection. Keep calm and remember you are not responsible for their feelings. Don't get involved in an argument of justifying yourself. Just keep calm, even if you feel differently inside.
The OP is certainly the object of her neighbours' projection of their feelings about themselves. They really want her to feel all the guilt and anger they feel at themselves for letting their child play in the road and have an accident. As soon as she said she does not use her front door they were ready to jump. They probably do it in other situations all the time.
It's also interesting how some people on here project blame on the OP for not answering her front door. In experimental psychology it would be said she had 'learned' not to answer the front door by getting so much negative feedback from doing so. Thus she had made an adaptive choice about that part of her environment- in psychological terms. In everyday life, she simply has the right to choose how to respond. She does not have a duty to answer that door any more than we have a duty to answer the phone every time it rings. So why do people attack her for not answering? They are projecting their own feelings. They either feel guilty and want her to feel guilty or they have a need to know who is at the door, come what may. But they are being irrational. It is her door. Nobody can blame her for not answering it. Also there is the important point she did not know who it was or why they knocked and they did not bother to try and get to her by the back door which they would have known about.
If you want to learn about projection, there's a brilliant short talk by Stephanie Lyn: Understanding Projection and How to Handle it!