Identical Twins??

[b-rad]

  1.  Load your game.
  2. Load a lot with your couple you plan to breed, Sim A and Sim B.
  3. Have Sim B get pregnant with Sim A's baby.
  4. Have Sim B give birth to Sim A's baby, Baby C.
  5. Save and close the game entirely - shut down Sims 2.
  6. Load the game again.
  7. Without doing anything else first (i.e. without Rolling the Pacifier), load Sim A and Sim B's house.
  8. Have Sim B get pregnant again by Sim A.
  9. Have Sim B give birth to Sim A's second baby, Baby D.
  10. Baby D will be identical to Baby C.

all you have to do is read further i took this right out of it