Another question ... Doh!
Ha.
I've never had triplets. The fertility happiness reward describes having a better chance of having twins and triplets. So it suggests it is possible, already in the game without a cheat or mod. Is there something they eat or do that increases those chances?
In the Sims 2, eating cheesecake from the Seasons expansion pack guaranteed twins, even if the house was going to be full with the one baby. That was told to players in an email from EA as a fun fact/handy hint as a reward after registering that expansion pack - when they were still on CD/DVD.
I vaguely remember some people on here discussing if tomatoes or watermelon is eaten or such, it increases the chances of the baby being one gender or another. So is there something the pregnant mother eats for triplets? One time, one of my pregnant sims ate nothing but lobster thermidore ... the baby's favourite food turned out to be lobster thermidore. Ha! Anyway ...