Instructions
"The Sims 2"
Click your two Sims (one male, one female) and have them each ̶0;Relax̶1; on a bed large enough for two adult Sims.
Make your Sims ̶0;Cuddle on Bed̶1; from the interaction menu.
Make your Sims ̶0;Try for Baby.̶1; After they finish ̶0;Woo-Hooing,̶1; you should hear a five- to six-second nursery-music-like chime that indicates your female Sim is pregnant. Also look for her to get sick the next morning.
Press ̶0;Ctrl,̶1; ̶0;Shift̶1; and ̶0;C̶1; simultaneously to bring up the cheat entry box.
Type ̶0;forcetwins̶1; (without the quotation marks) and press enter. Your pregnant Sim will now give birth to twins approximately three days later.
"The Sims 3"
Click the treasure chest-shaped icon in the bottom right of your screen while controlling a female Sim.
Check your lifetime rewards points. You will need 10,000 to proceed. Click ̶0;Lifetime Rewards̶1; if you have at least 10,000 points.
Scroll to the ̶0;Fertility Treatment̶1; reward, select it and click ̶0;Purchase.̶1;
̶0;Try for Baby̶1; (follow the same steps as in ̶0;The Sims 2̶1;) and there̵7;s a high chance your Sim will give birth to twins or triplets.