Lots of good ideas so far.
One problem as one comes to philosophy from religion is an unconscious and persistent (the more unconscious, the more persistent) tendency to ask religious questions and expect religious answers from philosophy.
Revelation and tradition per se have no authority in the realm of philosophy; they are not banned from it either, only they will be questioned and will have to argue their point on the marketplace like everybody else. The keyword being dialogue -- which includes a measure of agôn, "struggle," like in discussion or debate.
So a philosophical reply to your request might well consist in questions: why just one master? why a proper name? why ancient?
The world of philosophers has always been old (and new in another sense). Ours is older (and perhaps newer too). This is a difference within the difference, which must be taken into account as well.
Paraphrasing from Nietzsche (about deity), I would suggest that the essence of philosophy is that there are philosophers, not one philosopher. And only by exposing ourselves to their differences (which are contextual differences, in time, place, language, culture, before being differences in opinions or systems) can we learn to think with them and against them.
In French we have a number of good, interesting and lively introductions to ancient and modern philosophy for children, suited to their age. I don't know of anything equivalent in English but I'm sure there is.