It's all in the language and the concreteness of the examples. Philosophy most broadly is thinking about thinking. First step is to think, to learn to think. (And If anyone knows any place this was taught, please describe it here.) And as well that there's good evidence that children's brains may not be up to aspects of the various tasks that thinking about thinking may require.
I do not have it in hand, but I am pretty sure that Aristotle remarked that philosophy isn't for children. — tim wood
A philosopher can be someone who has studied the works of others and they need not really have their own ideas - they are essentially scholars if philosophy who regurgitate the words and thoughts of others in various ways (some more uniquely than others). — I like sushi
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