Well, the 'New Beginning' box set might be a good start, as you get two Doctors and the Master. I'd say your best bet would be to track down an episode guide online, and either you, or you and your son go over the episode descriptions and see which stories he finds interesting.
Now, episodes that a fan of the current series might relate to that are out on dvd:
The Time Warrior: Introduced both Sarah Jane and the Sontarans. Plus its just a fun story.
The Hand of Fear: Sarahs final story.
Invasion of Time: A bit long, but its another Sontaran story set on Gallifrey.
The Invasion or Earthshock: Two of the best Cybermen stories. (The first is in black and white and maybe a bit dated, but its still a good story)
The Five Doctors: Pretty much has it all. Gallifrey, the Master, most of the Doctors, Cybermen, and a Dalek. Plus the latest re-release has some nice extras about the show during the 80's, and even a silly David Tennant commentary.
Genesis of the Daleks or Remembrance of the Daleks: The Daleks weren't quite as impressive back then, but they're still decent stories.
Now, episodes that a fan of the current series might relate to that are out on dvd:
The Time Warrior: Introduced both Sarah Jane and the Sontarans. Plus its just a fun story.
The Hand of Fear: Sarahs final story.
Invasion of Time: A bit long, but its another Sontaran story set on Gallifrey.
The Invasion or Earthshock: Two of the best Cybermen stories. (The first is in black and white and maybe a bit dated, but its still a good story)
The Five Doctors: Pretty much has it all. Gallifrey, the Master, most of the Doctors, Cybermen, and a Dalek. Plus the latest re-release has some nice extras about the show during the 80's, and even a silly David Tennant commentary.
Genesis of the Daleks or Remembrance of the Daleks: The Daleks weren't quite as impressive back then, but they're still decent stories.
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