When your child asks you something like that, the first reaction is to freeze. Most likely, you do not know how to react, nor what to say, because It's something that you don't even explain yourself.
In situations like this, do not blame yourself if you do not give the "appropriate" answer, surely you will say what comes from your heart. Sometimes with a "Honey, I don't know" is said more than with a lengthy explanation. But with this world we live in, perhaps it is good that we ask ourselves this question, so that it does not take us by surprise.
What is it to be bad people?
It will depend a lot on the age of the child and the moral education he receives, what he understands by bad people. At certain ages they do not yet have a formed morality and they will depend on the knowledge of the adult to distinguish good from evil.
Depending on what you instill in your children, they can be bad people, those who take drugs, those who steal, those who kill or those who are simply different. Anyone can be bad people depending on the morality you are teaching your child.
This may be a bad girl
It is for this reason that it is so difficult to answer the original question that is posed. Because if we refer to Why do bad people exist?, Referring to someone who is different in some sense that we consider negative, we can always choose to say that there must be diversity. However, if it refers to the people who kill, it is somewhat more complex to answer.
How to face that question
First you have to assimilate what your child asks you. Once you really understand the depth of what he's asking, ask yourself the question and value the answer well.
As we said before, it is not the same for your son to ask you that question when he is 4 years old and his partner stole some cookies, than if a slightly older child asks you because he learned that there are people who murder or abuse children of your age.
You must be understanding with the situation and with the sensitivity of your child at that moment, to tailor your answer well. A child of about 4 or 5 years old may consider things like that the one who kills is just as bad as the one who does not pick up the dirty socks from the floor, if you do not explain it properly.
In the slightest case, we can always talk about what people are not really bad, that they are good by nature and that something in their education causes them to take the wrong behaviors. In the most serious case, it is somewhat more complex.
Putting us in the worst.
If we are in a situation where we have to explain to our child why there are people who kill or abuse children their age or younger it is very important that we take into account our child's sensitivity to the subjectIf your question is because you saw something at school or through the media, if it is something you heard about or if, unfortunately, it is something that has happened to someone close to you.
This is the turning point that will define the intensity and depth of our response. If it is something you know from hearsay, the important thing is not to lie to him, but it is advisable not to give it too much importance. This is because we could create a feeling of insecurity or fear, which is not healthy for our child.
In case it is as a consequence of something related to someone close, we insist on not lying. The response must be adapted to the age and degree of understanding of the child, but without distorting reality.
At this point the child already knows what happened and the only thing you have to try, whatever the answer, make sure that our child assumes what happened as naturally as possible, whether it is a sad death o an abuse. We must always try not to harm the child when dealing with these issues and be sensitive to the degree of understanding they have at each age.
Once our child has understood the facts, he will ask the question again and We will give the answer that we consider adapting to our own morality. There is no standard answer, because there is no logical reason for people to hurt others.