Before suggesting how to explain the topic of philosophy to children, it should be noted that there will be many adults that would not know the answer to this question. When I tell people I study philosophy, many of my friends will ask “what do you do in that?”
Philosophy comes from the latin phrase “philio sophia” which translates as: “the love of wisdom”. So, the goal of philosophy is to get knowledge, which of course raises the question of “how do we get knowledge”. The way we can get knowledge, is by being able to give a sound argument for what we are trying to know is true or false (in my tutorials regarding validity and soundness this is explained in more detail).
For the purpose of explaining to adults, philosophy can be explained as attempting to get knowledge about questions that are not typically trying to be answered in the sciences. Such as: what is the right thing to do, what is a just society, is there a God, do we have free will, can we truly know anything, and so on.
This is of course a terrible way to explain it to a child, as you would surely be met with a blank stare. So, the best way I would explain philosophy to children as trying to get to know things by being able to tell us why, or giving good reasons.
In primary school ethics classes, the cirriculum embraces such an approach. So, if a child asks “what is philosophy?” I would say trying to get to know things by giving good reasons.
Thanks for the relevant and interesting question,