I'd show the first episode of An Unearthly Child just to see how it started. Ignore the rest. The Pyramids of Mars was my first story 30 years ago so I think that worked I used Talons on my niece and nephew and they watch when they can but not as devoted. Busy teenage lives, I guess.
Other Doctors: THe Aztecs, Tomb of the Cybermen, Time Warrior, The Visitation/Black Orchid, Mark of the Rani, Remembrance of the Daleks